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The Practical Guide to Your RV Gray Water Tank

The RV gray water tank is part of the RV sewer system. Anytime you utilize a sink or shower within the RV, the dirty water collects in the gray water tank.

This receptacle differs from the black water tank, which collects wastewater from your RV toilet

grey tanks in RV Frame at factory
Grey tanks can be any color, but are usually black. These tanks are located under the RV floor and are where water from your sink, shower, and any other non-transit drain go.

How an RV Gray Water Tank Works

Simply put, the gray water tank collects the water as it drains from the sinks and shower in your RV. This includes soapy water from washing hands and bathing, as well as small bits of food or grease from dishwashing. The tank holds this water until you can adequately drain it.

Tank Capacity

The capacity of any gray water tank is dependent upon the specific RV. You can find your tank’s capacity in the RV manual. 

The vast majority of RVs also have a gauge that depicts the gray tank’s current level. Keep a very close eye on your gray water tank gauge throughout your adventures, and always dump the tank as needed. Otherwise, you may be dealing with an untimely (and frustrating!) backup. 

How Often Do You Need to Dump Gray Water?

If you are fully hooked up you can leave your grey tank open to drain directly out to the sewer. However, if you are using the RV without hookups or sewer, you drain the grey when it fills. Usually, when using off-grid, this coincides with running out of fresh water.

sewer dump hose
Note the smaller pipe and valve on the left, this is the grey tank. The grey tank is not always a smaller pipe but it is never a bigger pipe. They should be labeled but when in doubt the smaller pipe indicates grey tank.

Some RV owners may need to dump their gray water a few times a week. Others can go multiple weeks. With our 75 gallon grey tanks on our large RV’s we have gone 2 weeks pretty easily when being conservative with water. However, in our smaller truck camper with only 25 gallons of grey, we have to dump about every 4 days.

How to Know When Your RV Gray Water Tank Is Full

Your RV gray water gauge will show when it’s nearing full. If it’s not working correctly, you may discover the tank is full if the shower water begins to back up, usually in the shower. Seeing gray water backflow up your shower drain might be concerning, but it usually doesn’t mean anything is wrong. Most of the time, it merely indicates that you’re overdue to drain the gray tank. 

The water will back up into the lowest drain first, and it’s important to know which one this is. In most RVs this is the shower drain.

Dumping Your Gray Water

Dumping your gray water tank is reasonably straightforward, especially after some practice. The key is to be patient, thorough, and use the correct tools. 

First, you’ll need to locate the gray water valve on the outside of your RV, which should be clearly labeled. If it’s not clearly labeled, the valve is usually on the smaller of two pipes. After putting on gloves, hook your sewer hose up to the gray water valve and secure the other side of the hose to the sewer drain at a designated dumping station (never dump your gray water on the ground!). 

rv grey water and black water dumping

Next, check that you’ve tightly fastened both ends of the hose. Pull the valve to allow the tank to drain completely. When you can no longer hear any water moving through the hose, it’s safe to close the valve completely. 

Finally, disconnect the hoses from both the gray water valve and the sewer drain. For best results, flush the black water tank first and then the gray water tank. This will help to dislodge and remove any solid waste in the sewer hose. It’s also smart to rinse the gray water tank after dumping, using either a flush valve or a tank rinser.  

Cleaning Your Gray Water Tank

To keep a well-maintained gray water tank, cleaning it periodically is imperative. Don’t wait for your gray water tank to smell before giving it a good clean! Instead, schedule time to clean the tanks and try to do so when you’re driving a long distance. 

To clean the tank, add a half-cup of an RV-specific cleaning agent to a half-full gray water tank, along with a half-cup of dish or laundry detergent. If you have smell issues, using a bacteria-based tank cleaner can also help.

Getaway Couple Tank Tune-Up: RV Toilet Treatment...
  • ODOR CONTROL: Eliminate odors with our powerful RV holding tank...
  • WASTE DIGESTION: Power through waste with our advanced formula...
  • EASY TO USE: A single dose of powder not only cleans sensor...

After adding the cleaning agent, hit the road! The sloshing movement of water in the tank will help break down buildup. The gray water and cleaning solution should then sit in the tank for another 24 – 48 hours before draining. 

Odor Troubleshooting and Prevention Tips

Grey tanks can smell terrible, sometimes worse than black tanks! As long as your plumbing is working correctly however these smells should be contained. If you are getting smell in the RV its possible that air admittance valves, or P traps are not working properly. Some RV’s do not have P traps and will smell when going down the road. Every European RV we have rented has been this way and its critical to install drain plugs to stop the odor coming into the RV before driving.

If you begin to smell an odor coming from your gray water tank, you can also use any number of products specifically designed to eliminate odor. Most of these products also work to remove buildup. It’s imperative to follow the directions on these products for good results.

Happy Campers Organic Holding Tank Treatment works well at eliminating odors.

Happy Campers RV Toilet Treatment - 64 Black or...
  • ODOR FREE: Eliminates odors in the RV holding tank. Absolutely no...
  • Septic tank friendly
  • EFFECTIVE: In extreme hot & cold temperatures ( over 100 Deg)

Caring for Your RV Gray Water Tank Is Crucial

Understanding and adequately caring for the gray water tank in your RV is crucial. Before beginning your first RV adventure, note the tank’s capacity. Learn how to dump and clean the tank properly and what to do if unpleasant odors arise.

With this knowledge, you’ll be better prepared to tackle any gray water tank maintenance or hiccups along the way. 

rv sewer hose to dump gray water tank and black water tank

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Not So Free

Monday 22nd of February 2021

I like the Geo Method, You can google it. It basically uses water softener and bleach in both tanks as well as detergent in the black tank. I've used it in the last to RVs I've had and never had a clog problem. It even *kinda* keeps the sensors working.

Mortons on the Move

Tuesday 23rd of February 2021

Thanks for the tip!

Thurman Whiteley

Monday 22nd of February 2021

One way that I have discovered and use all the time is Paper plates ect. It reduces my water use and saves my Grey water tank from filling to quickly while boondooking.

Mortons on the Move

Monday 22nd of February 2021

Doing dishes less often will definitely help! We use a touch faucet when we do dishes, so the water isn't running constantly. Other people wash dishes in a separate basin so they can toss the dishwater outside; however, this is only recommended if you're using biodegradable soap.