RV Grey Water Tank – The Ultimate Guide: Read This First

Last updated on May 17th, 2021 at 10:34 am. Originally published on November 15th, 2019

When it comes to your RV’s plumbing system, not everything is black and white. Your grey water tank is the one that holds the waste water that comes from your sinks and showers — that is, everything other than the toilet. It’s the relatively clean waste water that includes soap, dirt, and food particles. And your RV grey water tank is the place it goes after it disappears down the drain… which does require some basic maintenance and cleaning. Here’s how to take care of the grey water tank on your RV!

1. What is an RV grey water tank?

Grey water tanks are where all the grey water in your RV goes.

Grey water is all the water used in your RV, except what goes to flush the toilet. That water is called black water. The water used for everything else — showering, cooking, washing dishes, and all other water-related activities — goes into the grey water tank.

Both grey and black water tanks drain into the same outlet but have different valves.

Some RVs are being built with a combination black and grey water tank. This makes the plumbing costs of manufacturers go down. This combined tank needs to be very large, which may be a problem in a vehicle, so the separate tanks are most common.

2. How do I clean my RV grey water tank?

RV Grey Water Tank Cleaning
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Since your RV’s grey water tank doesn’t hold very stinky contents, it doesn’t need the same kind of powerful, waste-dissolving tank chemicals your black tank does. That said, there are still grey water tank treatment chemicals that can help keep down odors if you find your tank is beginning to stink.

Just as with your black tanks, you want to make sure you regularly empty and drain your RV’s grey water tank — though it’s a good idea to drain it after your black tank, all that relatively clean, soapy water can flush your sewer hose of the truly icky stuff. Ideally, you should keep the valve closed, and allow the tank to fill up before dumping it. That gives you extra help from gravity, as well as keeping you from the messy situation that can result from leaving both valves open and draining when you’re hooked up at camp. (In short: the black tank ends up draining all the liquid waste, but solids get stuck, and you won’t have any grey water available to help the rinsing process!)

It’s not as common to have an RV grey water tank clogged, but if you do, you’ll want to use a gentle cleaning treatment rather than trying to snake the line. (Your RV’s plumbing system is different from the one you have at home!) Some campers report success using a mild dish detergent, like Dawn, along with hot water, to help break down greasy buildup. Let the hot water run and attempt to dump your tanks when they’re totally full.

3. How often should you dump and empty your grey water tank?

How to dump RV Grey Water Tank

Just like the black water tank, your grey water tank will gradually fill up over time as you go through the day-to-day adventure of camping. Each time you wash your hands, clean up after dinner, or tank an onboard shower, your grey water tank will collect the waste and begin to fill.

However, it’s hard to gauge how frequently you’ll need to dump your tanks because every camper is different. For instance, if you travel alone and most often shower at the campground facilities (rather than in your unit), you might be able to go a week or more without draining your grey water tank. On the other hand, if you’re traveling with a family and you all shower onboard everyday, you’re going to find yourself needing to drain your grey water tanks more regularly! Most RVs will have a tank holding sensor which will help alert you to when your tanks are filling up. However, on some smaller travel trailers, like Casitas, you might not know until your drains… well, stop draining. Either way, you’ll figure it out!

4. How do I dump my waste from my grey Water Tank?

How to dump RV Grey Water Tank waste

So, wondering how to remove grey water tank from your RV?

Dumping your tanks is actually super simple — and not at all the big mess most campers fear the first time they go about it. (That is, not unless something goes terribly wrong!)

To empty your holding tanks:

  1. Always empty the black water first.
  2. Wear rubber gloves at the least. You will not get splashed, if you are very careful.
  3. Remove the cap that covers the holding tank outlets, and connect your sewer hose.
  4. Put your sewer hose in the dump hole, at least four or five inches deep.
  5. Secure it in place. You can use a brick or the cover of the dumping station to secure the hose firmly.
  6. You can now open the black water valve. When the tank is empty, open the grey water tank valve.
  7. Flush your tanks by refilling them, and draining them again.
  8. Close your valves, and disconnect the hose from the outlet.
  9. Lift the sewer hose from the end of the RV to the dump hole, so as to get rid of any remaining water in the hose.
  10. Run water in it, if available, to rinse it thoroughly.
  11. Disconnect the hose from the hole, and rinse the area around it, in case some spillage happened. Cover the hole.
  12. Store your sewer hose.
  13. Add RV water tank treatment to your tanks, and you are done emptying your holding tanks.

Be sure you’re dumping in a designated city sewer connection only! Although grey water may be less toxic than black water (and is even legal to dump on the ground in some states), it’s always the best practice to dump your tanks into the actual sewer, where the water can be treated and reused. Stealth RV grey water dumping happens all the time, but most RVers would never admit to doing it. It is usually done at night, and in barren locations.

5. What is RV grey tank flushing?

Just as your black water tank does, your RV’s grey water tank may come with a flush system — though power-washing the tank isn’t as critical as it is in the case of black tanks, which hold much more potent waste. You can thoroughly clean your RV’s grey tank by running it through with soapy water or even a heavily diluted bleach solution, and some campers also add ice to the mix to help scrub the inside of the tanks.
If you utilize one of these homemade tank cleaning methods, like pouring ice down your sink or shower, you’ll want to take a drive before you dump your tanks in order to slosh the ice around inside your system and do its work. Again, be sure to dump in a designated city sewer! You don’t want to pour a lot of detergent and food debris onto the ground. Be sure to clean and sanitize your RV grey water tank at least once every year, to keep it from developing an odor.

6. Portable RV waste tanks

Portable RV Grey Water Tanks
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Some RV owners find it a chore to disconnect their rigs to drive to a dump station. Portable holding tanks come in handy in such scenarios. This is easy enough to do when emptying the grey water holding tank. Ensure that your portable tank is large enough for the task at hand, or be prepared to take a few trips to and from the RV to the dump hole.

Frequently Asked Questions about RV grey Water Tanks!

Here are some answers to campers’ most common questions about RV grey water tanks to finish this post out.

What’s the difference between gray water and black water?

Black water is the very dirty waste water that’s collected from what you flush down the toilet, including human waste and toilet paper. Gray water, on the other hand, is the relatively clean waste water collected from your sink and shower drains.

How accurate are the tank monitors?

The accuracy of your tank monitors, if you have them, depends on how clean they are! Although grey water tanks tend to build up less debris than black water tanks do, they can still benefit from a good scrubbing. Here’s how to clean your RV’s holding tank sensors.

Best practices for dumping?

As mentioned above, it’s best to wait until your tank is full, or nearly full, before you dump it, as it adds more pressure to thoroughly flush out the tank and hose. You’ll also want to dump your black tank first so you can utilize your gray water to clean out the sewer hose afterward. View our RV Dump Stations page and sort by State and Zip Code for a list of RV Dump Stations near you.

What are some tank maintenance tips?

When it comes to your gray water tank, be sure to dump it in designated city sewer connections as opposed to giving in to the “stealth” dumping option. And if you do notice a smell coming from your sink and shower drains, consider adding grey water tank treating chemicals to keep odors down!

Does my toilet use affect anything?

Your toilet does not drain to the grey tank, and therefore does not affect anything about it. That said, always be sure to use specially-formulated RV toilet paper and proper black tank treatment chemicals in your RV’s toilet, and avoid flushing any garbage or debris.

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