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The Ultimate Guide To Your RV Gray Water Tank

Kelly Headshot

By Kelly Beasley

We live in miraculous times, my friends.

For instance, isn't it a minor miracle that one can take a rig on wheels anywhere and have all of the comforts of home with them? I mean, how cool is that?!

Top comforts usually include a toilet, sinks, and running water.

Class C Motorhome Interior

But here's a question: Where does that running water end up when no sewer hose is connected?

The used liquid certainly doesn't go straight onto the ground.

For those times when you are not connected to a dump station, your RV has waste tanks for those liquids.

These tanks store used liquids until dumped using a sewer hose.

The tanks are called the gray tank and the black tank. Let's look deeper into the tanks, specifically the gray water tank.

What Is A Grey Water Tank On An RV?

A grey water tank on an RV is one of at least three tanks a recreational vehicle typically has. It has a gray water tank (possibly two gray tanks) a fresh water tank, and a black water tank.

The grey water tank is simple. It captures any liquids like bathing water and dishwashing water that goes down your RV drains.

This includes your sink drains and your shower or tub drains.

Put simply, it catches all water used aside from the toilet water (which goes into the black tank).

How Does A Gray Water Tank Work?

Just like your house, your RV has a plumbing system. It has drains and pipes leading from those drains.

Instead of leading to a municipal sewer system or septic tank, RV pipes lead into a black tank or a gray water holding tank connected to the RV. Your sink and shower drain water goes into the gray water storage tank.

The liquids stay there until they can be dumped into an appropriate RV dump station using an RV grey water hose.

Class B+ motorhome parked by the ocean

How Do You Know Your RV Grey Water Tank Is Full?

You can tell that your RV gray tank is full in one of three ways:

  1. Your sink and or shower stops draining/backs up.
  2. Your RV gray tank sensors show full.
  3. You know approximately how long your RV can go by experience (often based upon how much of your fresh water tank you have used). Obviously, your RV grey water tank size will have a lot to do with how long it takes to fill up.

What Happens When Grey Water Tank Is Full?

When your grey water tank is full you will notice that water starts to backup into either a sink or the shower (RV grey water tank overflow).

This means the motorhome or travel trailer grey water tank needs dumping. Once it's full, take your RV to any official dump station to dump.

You can find RV dump stations for RV grey water holding tanks in many places.

They are in campgrounds, some gas stations, some parks, fairgrounds, and more.

Expect to pay a fee, usually ranging from $5 to $15 to dump your gray and black tank and fill your fresh water tank.

How Do I Stop My Gray Tank From Smelling?

To stop your gray tank from smelling, you must first figure out what is causing the odor to come into your RV. 99% of the time, when nothing is amiss, odors stay contained in the gray tank.

The cause of camper grey water tank odors can be any of the following:

  • A dirty P-trap/sink that needs cleaning
  • No water in your P-trap
  • A leak somewhere under the sink or in the pipes
  • Your air admittance valve (AAV) might be stuck open

The dirty P-trap is an easy fix. Just take it apart and clean the trap. Also, clean the pipe leading up to the drain.

If the water has evaporated from the P-trap while in storage, this causes odors from the RV gray water tank to float right into your RV.

Easy fix- run water down the drain to refill the P-trap.

It ALSO could be that you cover your sink with the sink cover. For SOME REASON, this makes my (Kelly) sink smell like the grey tank.

Thought it was my P-trap, but I cleaned it and my sink but it still stunk. I finally stopped using the cover, and the smell disappeared. Go figure.

For leaks, use your eyeballs. Check under your sink and other areas if you have access to the pipes leading to your grey tank.

Air admittance valve

Air admittance valve under sink

As for the air admittance valve, this vertical dead-end pipe is found under your RV sink.

It keeps suction from happening in your trailer or motorhome grey water tank, but the moving valve can get stuck and remain open instead of closing as it should.

Replacing your air admittance valve is an easy fix.

What Is The Best RV Grey Tank Cleaner?

Personally, the best gray water tank cleaner for us is NO tank cleaner.

In myself and Marshall's combined 14 years of being RV owners, we have never 'cleaned' our RV gray water tanks.

(OK, Marshall did clean his after 7.5 years of owning the same trailer to see how the process works.)

The gray water tank is one that rarely clogs.

Yes, the gray tank sensors might read wrong if they get gunked up. This would be a reason to do a cleaning.

(Though, because RV holding tank sensors are so notorious for failing, most RV owners just learn to know how long they can go without dumping before the gray water tank gets full, instead of trying to fix the sensor issue.)

RV owners are much more likely to have their RV black tank clogged than their RV grey water clogged.

To clean your RV sensors, figure out which sensor keeps reading wrong. It's often the lowest as it sits in dirty water the most and has the most water touching it.

Still, figure out which one reads incorrectly.

Dawn dishwashing detergent

Then fill your gray tank almost all the way full with water (warm/hot preferably if you have access to that much hot water). You want to cover all sensors, so you won't need to fill the tank, just cover the topmost sensor.

Put in at least 20 ounces of dish soap into the tank (preferably a brand that cuts grease - Dawn Ultra is a recommended brand).

Fill the tank a bit more to agitate the soap in the tank. You may see foam coming up through a sink or shower drain. Again, you don't need to completely fill the tank with water - just up past the topmost sensor.

If possible, take your RV out for a short ride to slosh it around. This is not mandatory but couldn't hurt. Only do if it's easy to move your rig.

Let the soapy water sit overnight. Drain your gray tank. Rinse it a couple of times by filling it up with water and draining it.

Check to see if your tank sensors are reading correctly if this was the reason you wanted to clean the tank. If they aren't reading correctly, repeat this procedure.

It's our opinion that you do not need a dedicated product to clean your RV gray water tank. All you should have in the gray water tank are food particles, grease, and hair.

You only need water and the correct soap to clean an RV gray water tank.

Marshall Cleans His Gray Tank

After 7 1/2 years of owning the same Lance travel trailer, I (Marshall) cleaned my gray tank for the first time. Not because there was anything wrong, but because I wanted to see how the process worked.

I purchased a large bottle (90 ounces) of Dawn Ultra from Costco and did the above procedure with a little over 1/3 of the bottle (more than 30 ounces). My gray tank has a 45-gallon capacity.

After letting the Dawn and water mixture sit in the gray tank ( filled up with freshwater) for 24 hours, I dumped and filled it up again to rinse it out. Then dumped and filled and did a final dump, for a total of 2 tank rinses.

With the last rinse, the water was running clear, with no gray sludge that you usually see as the tank drains the last of the water.

I rarely look at the gray tank levels using the onboard monitoring system as they often read incorrectly. Still, I did notice that they seemed to be reading accurately before starting this procedure.

I have no clue how long they've been reading correctly, as most times when I do check (once in a blue moon), they always read something other than empty when the tank is empty.

I wish the sensors had been reading inaccurately to see if this cleaning trick made them work properly. I'll have to wait until the gray tank sensors aren't reading accurately again and repeat this.

Overall, it was a painless process, and it appears to have cleaned the gunk out of the tank. However, without taking a look inside (which is impossible unless you have the proper tool), I'll never know how clean things got.

Your mileage may vary with this procedure, but it's worth a shot if your gray tank sensors aren't reading correctly.

Can I Put Bleach In My Grey Water Tank?

Yes, you can put bleach into your grey water tank, but it is not recommended.

First, you don't need to disinfect RV tanks made to hold bacteria, waste, and such. You only need to disinfect your freshwater tank.

Second, the bacteria that are in there may produce ammonia. Mixing ammonia and bleach is toxic. If the fumes get into your RV, that's not healthy for you.

Also consider that the bleach may not be good for the seals in the motorhome or trailer grey water tank drain valves.

Me? Marshall? We don't use anything in our grey water holding tanks. We have zero issues with our RV tanks and waste water.

Clorox bleach bottles

Why Is My RV Grey Tank Not Draining?

If your RV grey tank is not draining you may have a clog of some sort. (Or your sensors are telling you there is liquid in gray water holding tanks but you do not. Very common.)

Gray water tank clogs are pretty rare. If you KNOW you have liquids in your gray water tank but nothing comes out when you dump the tank, something is blocking the drain.

It has to be significant because the first drain solids go down in your camper is quite narrow.

Air Admittance Valve:

Check your air admittance valves under your kitchen and bathroom sink.

If one of them is stuck, there will be a vacuum in the gray water tank and the liquids won't be able to escape.

Air admittance valve

Air admittance valve under sink

Food/Grease/Soap/Hair Buildup:

As far as your kitchen sink goes, when you wash dishes, some food particles go down the drain. Food particles are small, right?

They can, though rare, accumulate in the gray water holding tank. Especially if you also put grease down your drains.

Soap and hair can also get into the gray water tank and cause buildup in pipes causing problems with your gray water dumping.

Construction Left Behind:

The other more common issue than one may think is that there is a disc left in some RV grey water tanks.

It's from when the worker drilled the hole for the pipe and then left the round disc inside your RV gray water tank.

The disc moves around and eventually gets sucked towards the exit tube and blocks the grey water holding tank drain.

Clogged Grey Water Tank Solutions:

Is The Gray Water Valve Stuck?

First, ensure that the valve that opens and closes that grey water storage tank is working correctly.

Hopefully, you have visual access to this under the RV.

It could be disconnected from the lever, or the pull lever might not be opening all the way.

RV sewer pipe outlet

Boiling Water:

If your valve is working correctly, try pouring boiling water down your kitchen sink drain and bathroom sink drain.

Add some dish washing soap or detergent (Dawn Ultra is a preferred brand). Best that what you use for washing dishes also de-greases.

The hot, soapy water or detergent dissolves any greasy or soapy blockage you may have in your holding tanks or tank or drain pipe. You may need to do more than one treatment.

Leave for about 15 minutes before draining.

You don't want the hot wastewater to cool much, or the oils will solidify again, and some will stick back to the walls.

Pipe Flush Method:

We don't think this is very effective, but some have claimed it worked with their gray tanks.

If boiling water fails, you can try using your tank flush with a hose. If you don't have a flush, you can get a dump attachment with a flush. Give it a try. You won't lose anything.


If nothing worked so far, it would be great to get eyes down the drain or into the tank. If you can get a snake and attach a camera (waterproof) to the end, you can visually find the blockage.

This isn't the cheapest method, of course. A snake alone may break apart the clog. Never know till you try.

If all else fails, hire a professional to clean and de-clog your holding tanks before your next camping trip.

Liquid Tank Cleaner

When it comes to RV grey water tank cleaning, one of the above methods usually is enough to solve whatever issue you are experiencing. However, sometimes you need to take things up a notch.

If you have a stubborn case of your RV gray water tank not draining and you've tried some of the above methods to clear the blockage, you could try the Unique brand of tank cleaner.

This tank cleaner is specifically formulated to unclog holding tanks and should clear up any blockages (assuming you follow the instructions, duh!).

Unique tank cleaner


RVs in no frills campground

Camper gray water tanks capture everything that goes down the drains (sink/shower) of an RV. There the waste water is held until you dump it at dump stations using your RV sewer hose.

The reasons your grey water tank may need cleaning is if your sensors start reading wrong (which is pretty common), or if you start dealing with a nasty odor.

Follow the instructions above that explain how to clean a gray water tank. It's very simple and normally doesn't require a particular product.

That's it! Your RV grey water tank doesn't require much at all.

Keep hair, food, and grease from going down your drain as best you can, and you likely won't have any problems with your motorhome or trailer gray water tank!

Kelly Headshot

I dedicated myself to living the full-time RV life for over 6.5 years, immersing myself in the unique quirks and joys of the boondocking lifestyle and gaining a wealth of knowledge and experience along the way. In December 2020, my business partner and I made the transition to part-time RVing, but in January 2023, we hit the road once again, this time in our trusty vans. My mission is to help others embrace the RVing lifestyle with confidence and excitement, armed with the knowledge and resources needed to make the most of their adventures. I believe that the more you know, the more you can truly appreciate and enjoy the freedom and flexibility of the open road.

  • If I don’t use my toilet in my RV but just use the shower and sinks in the bathroom and kitchen that would be considered gray water correct and I could dump that outside with a button I’m supposing .
    I am new to this

    • Hi Lisa,

      Technically, that’s correct.

      However, understand that it is not legal to dump grey water on the ground, street, or public lands in many places. Check with the local ordinances or laws to know if and where you are legally allowed to dump your grey water.

      Also, it’s usually only legal if you use all non-toxic agents. AKA no harsh chemicals, shampoos, etc should go down the gray tank.

      And usually it’s not a push button, but a lever you pull to release the goods! Cheers-

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