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What To Do When An RV Waste Tank (Black/Grey) Won’t Drain

Reasons Black & Grey RV Holding Tanks Clog

So you’ve taken your RV to the dump only to find that the black or grey tank will only empty a few gallons, or not at all.

This is a common problem for RV owners, especially those who are dumping a used RV or trailer for the first time.

Related Product: Dump your RV without moving by using a Camco Rhino Portable RV Waste Tank (click to view on Amazon)

Improper RV holding tank maintenance is one of the major causes for clogged black tanks, and the previous owner may not have taken proper care of their RV waste tanks.

There are three major causes of blocked or clogged RV waste tanks.

  1. Broken Gate Valve or T-Handle
  2. Inorganic Blockage (flushable wipes, foreign objects, things like that)
  3. Organic Blockage (valve was left open for a long time, causing things to dry and harden, creating a blockage)

In this article, I’ll go through some of the main things you can do to unclog a black or grey tank yourself.

I’ll start with things you can do with limited equipment in case you are standing at the RV dump station right now reading this article, trying to unclog a black tank.

See Also: Best Septic Safe RV Toilet Paper Brands Reviewed

How To Unclog An RV Black Tank

No matter what the reason is for a clogged black tank, there are a few things you can try right now to get things flowing again.

If none of these things work, you may need to resort to the more time-consuming methods outlined further on in this article.

Make Sure The Gate Valve Is Open

The first thing you need to check for is if the gate valve is open or not.

Unless you have a serious hard buildup and blockage right at the valve opening of your black tank, there should be at least some liquid that comes out.

If absolutely nothing comes out when you open your black tank, the problem may be the gate valve.

While it’s not a common problem, it’s worth checking out.

You should be able to see the gate pull out when you pull on the t-handle.

If you have a trailer like mine where you can’t see the gate move in or out the t-handle should have a bit of resistance when you pull open the gate valve.

See Also: Dump RV Through A Garden Hose At Home! RV Macerator Pump Use

Sewer outlet on an RV with the correct gate valves labeled
One reason for a grey or black tank that won’t drain is a broken gate valve.

If the t-handle can move in or out easily and seems like it’s not attached to anything, that means the gate valve isn’t opening.

If the t-handle is broken, you may have to take some pliers and open the gate valve yourself.

If the waste tank drains like normal, you have found your issue.

Back Flush It

The most common problem will be a clog of some sort right at the valve opening.

If you are lucky, it’s just a buildup of toilet paper and other organic stuff (aka number two).

You need to flush the tank out backward from the valve opening to displace the clog and hopefully break it apart.

If you have a black tank flush on your RV, travel trailer, or 5th-wheel this may not work because you need to attack the clog from the other end.

I suggest always having a sewer tank rinser like the Camco Rhino Blaster Pro W/Gate Valve (click to view on Amazon) for an emergency situation like this one.

Camco 39085 Rhino Blaster Pro Holding Tank Rinser w/Gate Valve

Holding tank back flush products like these can be useful in holding tank maintenance and for breaking up or even snaking out clogs.

If you already have one of these, attach it and start shooting water into the clogged black tank.

It should either break up the clog or at least move it to allow the rest of the black tank to drain.

See Also: Best RV Portable Waste Tanks For Black & Grey Water

If you don’t have a black tank flush attachment like this, you can also try to flush water into the black tank by opening the grey tank all the way for a few seconds.

When both valves are open, some of the water from the grey tank should flow into the black tank and put pressure on the clog. If you are lucky, it will break it up.

Try opening the grey tank valve while the black tank valve is open a few times.

If the grey tank is empty, fill it up all the way so you can get a lot of pressure when you open it.

Hopefully, this method will get your black tank draining again.

As a last resort, you can always use a hose. This method isn’t always optimal because if the clog gets broken up and you don’t have the sewer hose attached, it’s going to be a mess.

Be ready to close the gate valve once the clog is broken so you can put the sewer hose back and get things diverted to where they’re supposed to go.

Check The Roof Vent

If back flushing didn’t work, there are still a few things you can check or try before getting into the more time-consuming methods for unblocking a clogged black tank.

If your black tank is slowly draining but not flowing out as fast as it should, you may have a clogged air vent.

This issue is more common than you think, especially if you are camping or storing your RV in an area with lots of wasps. They may have built a nest in your vent.

You can check this by having someone go into the RV or trailer and flush the toilet while the water pump is off.

If your black tank suddenly flows more and it seems like a vacuum seal was broken by allowing air into the tank, then you know the air vent is clogged.

See Also: How To Install Solar Panel On RV Roof & Connect To Battery

Once you’ve emptied your black tank with the toilet open, you can try to unclog the air vent by removing the cap to it on the roof and sticking a hose down to break up whatever is clogging it.

If your roof cap was on properly, it shouldn’t be anything more than a wasps’ nest or some toilet paper that found its way into the vent.

Note there is both a grey and a black tank vent on the roof of an RV.

Normally, the smell indicates which one is which, but if you don’t know for sure, you can always flush out both of them.

Once you are done flushing out the vent, you will need to reseal the screws on the cap.

Self Leveling Lap Sealant by Dicor (click to view on Amazon) is the top choice of most RVers for sealing anything on a camper roof.

You can also use Eternabond Roof Tape (click to view on Amazon).

It’s easier to store than lap sealant, it can also seal pretty much anything on an RV roof, and there’s a lot less mess.

Dump Water Into The Toilet

If back flushing the tank sort of worked and there is at least some black water draining out of the black tank, another thing you can try is to dump a 5-gallon bucket of water into the toilet.

The high velocity of water flushing into the black tank all at one time should break up the clog even more or possibly force out any foreign objects that were blocking it.

Don’t start with this method as it could make the clog worse. Only do this if you are getting some black water to come out of your black tank after back flushing it.

The Drive Around Method

If you’ve tried these things and the clog still won’t loosen up, you are going to have to use water, chemicals, and motion to loosen up the blockage.

If you have recently bought a used trailer and haven’t taken it camping yet, do this to get rid of anything in the RV waste tanks the previous owner may have left you with.

You also should do this to get your black tank good and clean before winterizing it as well.

First, make sure the black tank valve is closed. Some people don’t realize they are open and have been using their black tank, which is a big reason clogs happen.

See Also: Best RV Sewer Hose Kits Reviewed & Rated

Next, you are going to need some chemicals.

You should always use some sort of black tank treatment like Camco RV Toilet Treatment (click to view on Amazon) or better yet Happy Campers Organic RV Holding Tank Treatment (click to view on Amazon).

You can find the Camco RV toilet treatment in almost any hardware or superstore, but if you have the chance to get the Happy Camper RV Tank Treatment, I recommend that one.

It may say organic on the packaging, but it’s one of the best RV toilet treatments out there and it can break down clogs like nothing else.

Get your 5-gallon bucket and fill it with hot water and about a half a cup of dish washing soap.

Cold water will work as well, but hot water is going to be more effective.

Take the RV holding tank treatment and dump about 2-3 times more than you normally would down the toilet.

Next, dump the 5 gallons of hot water + dish soap down the toilet as well.

If you have enough hot water to dump a few more 5 gallon buckets down the toilet, it’s a good idea to do that, especially if your waste tank is low on water.

If not, dump at least one more bucket of water down the toilet, even if it’s cold water.

It’s time to take your RV or trailer for a ride. You want to get the water sloshing around to break up anything and everything in your RV black tank.

You don’t have to go crazy and drive 50 mph down a washboard dirt road, but getting the trailer moving is going to be your best bet at breaking down the clog.

If you have the time, you can even let your trailer sit for a few days to let the chemical do the work.

If you don’t have the time for that, going for a good long drive may be all it takes.

Once you’ve driven around, try to dump the black tank again.

Hopefully, this has broken down any organic blockage or caused whatever was blocking the valve to come out.

You may need to implement some of the previous steps to get things going.

Snake It

There is one more thing you can do before calling a plumber and possibly taking apart the entire RV black tank valve system. You can snake it.

Just as a warning, if you have never used a drain snake before, you need to be really careful to not cause the snake to get bunched up in the pipe because the snake could get stuck as well.

Everything should work fairly easily and never use excessive force.

The main issue with snaking your black tank from the gate valve end is if you break up the clog you are going to have a ton of nasty raw sewage pouring out quickly.

If you’re not prepared, you may end up with a giant mess on your hands.

See Also: Best Portable Power Station/Solar Generator For Camping & RV

There are a few things you can do to minimize the mess and contain the black water coming out.

The simplest thing people do is drill a hole on the top of their sewer hose near the bayonet coupling.

This will, of course, destroy your sewer hose and you are going to need a backup one handy.

You can get a cheap sewer hose for this so you don’t destroy your nice one.

RV sewer hose connected to an RV black tank that has a clog
Drill the hole for the drain snake at the top of the sewer hose closest to the connector.

Once you’ve drilled a hole in the top, you can slip the snake in and start working it into the black tank.

Most black tanks have little distance between the main opening and the gate valve, so a short snake like the General Pipe Cleaners 3-Foot Toilet Auger (click to view on Amazon) with a 1/2 inch snake should work.

Make sure the snake goes in the correct tank.

Once you’ve got the main part of the snake through the hole you’ve made, I suggest using a rubber glove or at least a rag to stop sewage from leaking out the sides.

Now you can start snaking.

Once the clog has been hit and broken up, sewage should start flowing out right away.

Even though it’s going to be a mess, let some of it drain out to make sure it released the clog.

You don’t need to dump your entire black tank with the compromised sewer hose.

Once the clog has drained out, close the gate valve and switch the bad sewer hose with a good one and finish dumping your black tank.

See Also: Best Portable Foldable Solar Panel Chargers For Camping & RV

Another thing I’ve seen people do is use their RV black tank flush attachment to feed the drain snake through.

You may need to drill the part the hose attaches to make it big enough to allow the snake through.

This method works as well and you might not have to damage a sewer hose if you do this.

The drawback to this method is you may damage the RV black tank flush attachment if you are not careful and they can be more expensive than a new sewer hose.

porta potty company emptying rv that has a clogged black tank
Truck from a porta potty company unclogging the RV black tank from the inside.

Call The Professionals

The black tank on a family member’s 5th-wheel got clogged this summer.

We did what we could to fix it but the clog just wouldn’t break up. It ended up being a situation where we needed to call someone to help us.

The best option ended up being a porta potty company. Surprisingly enough, those kinds of companies actually dump RVs all the time.

They had a special attachment made specifically for RVs, and they could vacuum the clog out of the black tank and dump the rest of it at the same time.

There was no mess. We got the tank dumped, and the price was very reasonable.

If there’s no porta potty company around, your next option would be a plumber or RV repair shop.

Neither of those options sound great but if you’ve tried these things and nothing has worked, you may be out of options.

How To Unclog An RV Grey Tank

It’s less common for RV grey tanks to clog, but it happens. You can use any of these methods used to unclog an RV black tank.

The only thing I would change would be if you are going to use the water in the black tank to flush out a clog in the grey tank to make sure the black tank has been fully drained and cleaned as much as it can be.

You don’t want raw sewage going into your grey tank.

You can do this by emptying your black tank and flushing it out with a Camco Swivel Stick Black Tank Sprayer (click to view on Amazon).

Dumping a 5-gallon bucket full of water and dish soap down the toilet a few times will help clean it out as well.

Then fill the black tank with fresh water so you have something to flush into the clogged grey tank.

There is also no direct opening to the grey tank like there is to the black tank. It’s going to be harder to get a ton of water into the tank all at once.

First, put holding tank treatment into the kitchen sinks, bathroom sink, and bathtub and then try to dump as much water as you can down each drain all at the same time to get as much water flowing into the grey tank as possible.

Hopefully doing this will unclog your grey tank. If they don’t work, you can also use the snake method.

See Also: The One And Only Guide To RV Leveling Blocks

Final Thoughts On What To Do If The Black Or Grey Waste Tanks Won’t Drain

Things go wrong with RVs, travel trailers, and 5th-wheels all the time.

I’ve had to fix almost everything on my used travel trailer even after just a year of owning it. Having clogged holding/waste tanks is just another part of RV ownership.

Hopefully, being able to go camping or travel the world in an RV makes up for all the problems you experience along the way.

There are things you can do to properly maintain RV holding tanks so you never experience any clogs. You can read about that in this article here.

I hope at least one of these methods has worked for you and you haven’t given up on camping or RV life.

As a reminder, if you have bought a used RV, whether it was from a private seller or a dealer, make sure you fill the holding tanks with water and dump your RV before taking it camping.

You never know how someone else has treated their RV holding tanks and you can hopefully avoid any future clogs by cleaning your holding tanks really well before using them.

Have any more questions about RV black or grey tanks and fixing waste tank clogs? Leave a comment below.

by Jenni
Jenni grew up in a small town in Idaho. With a family that loves camping, she has been towing trailers since a very young age.

25 thoughts on “What To Do When An RV Waste Tank (Black/Grey) Won’t Drain”

  1. 2 tips from my RV days….
    1. Always carry spare valves….they only break when you are no where near an RV shop…
    2. I made a sprayer for the tanks from a female hose end epoxyed to a length of PVC sprinkler pie with a 360 degree sprinkler head on it….connected to a hose, I could stick it down through the toilet, or in through the drain pipe and and keep the inside of the tank clean….

      • I’m hoping someone can help me. I just recently bought a used 2008 carriage Domani, I do plan on living in this as my permanent home and waiting for an above ground septic portable tank to be delivered so we can hook it up but my problem is this, anytime I push the button on the RV to flush my black water tank nothing happens. It doesn’t even light up red to indicate that it is on like the gray water tank does. We’re trying to drain the black water tank but have push the button to turn it off now and nothing happens. I have watched numerous videos and everybody is talking about a switch or valve that you would have to turn on but for the life of me we cannot find this switch or that. Nowhere. Help please. Thank you

        • Hi Dottie,

          There could be a second switch somewhere between the gate valve and the main switch but it sounds like you may have blown a fuse.

          Drain Master electric gate valves usually have a 5 amp glass fuse (click to view on Amazon) somewhere between the switch and the battery. It’s probably closer to the battery so I would start looking there first.

          It could also be that the plug between the valve and the switch has come loose. It should be somewhere behind the switch. When you find it try pushing it together to see if that helps connect it better.

  2. This article solved my black tank mystery. On my first trip out with my brand new Jayco 28RL, I was attempting to empty the black tank, then the grey. I pulled the black tank lever and there was not much of a flow going through the clear elbow tube. (The black tank was over 3/4 full and should have been gushing out). After a short wave of panic I pulled one of the grey tank levers which seemed to open up the dam. I was relieved yet mystified why this happened after reviewing tons of videos on how to empty the tanks and in which order.
    I found your article which answered many questions.
    Thank you very much for posting the article.

    • No problem Mac, thanks so much for the comment.

      I’m glad you were able to get things working the way they should. Enjoy that new Jayco!

  3. I believe I have a broken valve. I have a 2018 Riverstone 39FKTH & the black tank valve was stiff & we used product dealer suggested & I back flushed. Been ok & then BAM! It’s like the handle isn’t pulling valve open.

    • Sounds like the part connecting the gate valve and the handle may have come loose. You will need to follow the black tank pipe and find where the gate valve is to see if something got disconnected.

      It could also be that flushing out the black tank and using some chemicals may have helped break up something that was on the inside of the valve. Normally they are pretty easy to open and close and you may have just gotten rid of whatever was making the valve stiff.

  4. I have a 2001 nomad travel trailer. .my buttons dont say black water it just says solids and i have it hooked up at a camp ground and the solids will only go down 2 out of the 4 lights. And when i look down my toilet i can see all this brown liquid. I have both valves opened up outside since im connected to the campground. I am on a fixed income. Is there anything i can do that is cheap to get this to empty all the way? Also im not sure how to get back to this if anyone replies.

    • Hi Britnee,

      Your black tank is most likely almost empty. A lot of the time the sensors on RV holding tanks will get blocked by something and they will display full or partly full even when not. My bet is that your black tank isn’t emptying all of the way because you are sitting either a little to one side or exactly level. Lots of RVs require you to be up higher on the opposite side of the drain to fully empty the tanks.

      I don’t recommend having the grey and black tank valves open at all times even when connected to a sewer at a campground. This allows for smells from the sewer to get into the RV through the drains. It’s also better for the black tank if it has at least 5 gallons of water in it at all times. When we stay at RV parks with hook ups we leave the sewer hose connected but only open the gate valves to drain the tanks when they get full. This helps prevent clogs and it will help the black tank drain better.

      • When i look down my toilet i see liquid and it looks as if its full? There seems to still be a lit of sewage in there. I dont know if i have some type of clog. When i move i can hear the sewage moving. So i dont know if i should buy something to eat away the toilet paper and other stuff if there?

        • Yes, you should always be using chemicals inside your black tank to break down toilet paper and solids. That’s part of the reason you shouldn’t have it open all of the time.

          I recommend getting the Happy Campers Holding Tank Treatment (click to view on Amazon). It’s one of the best holding tank treatments out there but you can also get other brands at local stores that are better than nothing.

          You may have a clog now that could be fixed by putting chemicals into the black tank and waiting a few days. Another good product to help break up clogs is the Camco holding tank rinser (click to view on Amazon). You attach it between the sewer outlet and your RV sewer hose, then using a regular garden hose you use it to shoot water into the black tank which will help break up whatever is blocking it.

          Using the Camco tank rinser and chemical should help get your black tank draining again. Once you get it drained you should close it, put a few gallons of fresh water in it, add black tank chemical, and only dump it when it’s full. This should help prevent any clogs in the future.

  5. I have a broken gate valve. Everything says to empty gray tank to replace gate valve. How do I do that when I can’t get it open

    • Hi William,

      Have you tried to open the gate valve with pliers? Sometimes you can still get a grip on part of the gate and work it open.

      If opening it isn’t possible you may have to start unscrewing the gate valve and use some buckets to catch what drains out of the grey tank until it’s empty. It’s going to be a long process but it may be the only way. At least it’s not the black tank.

  6. Hello, I am also having the issue Britney is having. I bought chemicals and waited for days. Nothing. Can you recommend a mobile person in the San Diego California area I could call?

    • Hi Jessica,

      If you don’t think you can try and snake the tank yourself you can always call a porta potty company, they normally have the resources required to remove waste from an RV holding tank. A plumber is another option but they might end up costing more.

  7. My gray tank won’t empty my black tank does i open gray tank nothing g comes out but under the back of rv the belly us so swollen looks like it’s gonna burst water has dripped underneath it all summer long ut drips worse right after I have done dishes I own a 88 kountry star don’t know what to do

    • Hi Terri,

      When it comes to the grey tank there isn’t normally a lot that can clog the outlet. Is the gate valve opening when you pull the lever or is it possibly broken? If it seems like it’s broken and not opening you may be able to use pliers to grip the valve part directly and get it to open. You can also just undo the bolts around the vavle to release at least some of the water to help relieve the pressure on the tank.

      You can also try opening the valve and sticking something like a hose up the pipe to see if you can clear what’s possibly blocking it.

  8. I think I’ve had every problem that your readers have all had and have always been helped by reading blogs like yours. One of the readers above had a simple fix for a problem I’ve had all summer. I haven’t been able to completely empty my black tank all year and it was because where I dump is not level. DUH! I didn’t change spots because it’s convenient but what I now do is drive up on about 4 inches of blocks to tip the trailer in the other direction! It’s now empty as empty can be.

    • We’ve had the exact same issue, I don’t know why dumps aren’t made to be level or lean toward the drain side.

      Glad this post and comments were helpful!

  9. nothing is coming out when i try to empty black and grey tanks had the black valve replaced about a month ago looked up train pipe with flash light pipe is closed off only a small trickle of clear water is trickling out grey handle is a bit stiff. would this indicate that the grey valve is broken if so how can I remove it

    • Hi Wayne,

      If the handle is stiff it sounds like the cable is binding somewhere or the gate valve is gummed up.

      Follow the cable that leads from the gray tank handle to the gate valve and make sure nothing is tied up or blocking the cable from working.
      You may need to access the gate valve and use pliers or something to get the valve to open so you can drain the tank. Then once it’s drained you can use drain valve lubricant (click to view on Amazon) to try and loosen it up.

      It’s strange that the black tank isn’t emptying even though the valve was replaced recently. Are you sure there’s not something blocking both of the tanks in the spot where they meet in the main pipe?

  10. For black or gray tanks, pour 1/2 to 1 cup of Cascade liquid gel dishwashing detergent down the toilet or kitchen sink drain, followed with a kettle full of boiling water. Let sit for 10 minutes. Add 5 gallons of water to the tank and then take your rv for a good drive all over town to let that tank’s contents slosh around the plumbing, then go home and drain, followed by rinsing the tank out twice. This worke every time for me. I rarely have any issues, live in my housecar full-time, never use those tank chemicals, use regular toilet paper and do not get poop pyramids in the tank. I only empty the tanks when they are full, black, then gray to clear out the sewer pipe. After emptying the tanks, In do add a few gallons of fresh water to the black tank before using it as this helps avoid buildups of solids. I hope this helps somebody. Cheers!


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