What is GREY Water in a Motorhome (RV)?

As a full-time motorhome enthusiast, I sure have produced a lot of grey water, and in this article, I will explain precisely what grey water is, or if you prefer to look at a video I have made on the subject, you have it right here above.

Grey water is all used water that does not go through the toilet (black water). Fresh water becomes grey water when used and goes down the shower drain, bathroom sink, kitchen sink, or via appliances like washing machines; it drains into a grey water holding tank.

So you are producing grey water when you, for example, are doing the dishes, taking a shower, washing your hands, or brushing your teeth. When doing these things, you use different types of products like soap, shampoo, and detergent, or when you are doing the dishes or cooking, there will be some food leftovers and grease that comes with it.

Since these might be products or things you should not empty anywhere in nature, they will drain down to the grey water holding tank so you can empty them at a suitable location.

Yes, it seems pretty straightforward, but what if “someone” pee in the shower (of course, you would never do that? blame it on the kids, maybe)? Is it still grey water, or should you treat the whole grey water tank as black water?

Is Urine Considered Grey Water?

My bathroom with separate shower that drains to the grey water tank and the toilet that goes to a cassette with black water.

Technically speaking, urine is black water and should not be mixed with grey water which it would be if “someone” would pee in the motorhome or RV shower.

But is it just pee? Yes, it is, but the problem is when the urine gets to the grey water holding tank, and it stays there mixed with the rest of the grey water for days, bacteria will start growing like crazy, which will cause strong odors from your grey water.

Sometimes these odors will even come up through the drains and give a strong smell inside the motorhome. Especially while driving when the grey water is moving around and splashing up the pipes; if you have a full tank, I’m talking from experience, but at least now we all know what that smell could be.

So with this in mind, maybe you travel with kids or “someone” peed in the shower; you should limit the time you hold the grey water in the tank so bacteria don’t start growing, and be more careful where you dump the grey water. It would be best to take extra sanitary precautions and frequently clean your grey water tank.

What Is a Grey Water Holding Tank?

My grey water holding tank is not insulated and is placed underneath my motorhome.

A grey water holding tank is a big tank where the grey water is stored until you empty it at a designated dump station. The grey water tank is usually placed underneath the motorhome or RV. Still, if you have a better-insulated motorhome suitable for winter camping, you typically have the grey water tank in an insulated area, most commonly within a double floor.

A grey water tank is usually about the same size as the fresh water tank; I have, for example, a 100 liter (26 gallons) grey and fresh water tank.

“When I run out of fresh water, it is also time to empty the grey water tank.”


What Happens When Grey Water Tank is Full?

Grey water will flow back up the shower drain when the grey water tank is full. If the tank is full and you keep using the water in the motorhome (RV), you will notice that grey water will start coming up in the shower drain since it is the lowest drain and the grey water need to go somewhere, so it goes back up the pipes and into the shower.

You should watch the grey water level if you don’t want a smelly and annoying experience with an over-full grey water tank. Most motorhomes or RVs have sensors built into the tanks that show you the grey water level so you can regularly check it quickly.

It is common to have problems with these sensors in both the grey water and black water holding tank, and I would recommend you to read my article about how you can fix these sensors but, more importantly, how to make sure they don’t stop working for you.

You can also check the total volume of your fresh and grey water tanks as they usually are about the same size, so then you can do like me and refill fresh water and empty grey water at the same time and not have to worry about it.

How to Empty Grey Water From a Motorhome (RV)?

A wrench has replaced my drain valve handle after it fell off a few days ago. (check, so yours is not loose)

Position your motorhome, especially the grey water tank drain valve, above a grey water dump station and open the valve. If you can’t drive and place your valve directly above the grey water dump station, you can connect a hose to your drain valve and put the other end of the hose into the dump station.

The drain valve is usually just a handle that you turn 90 degrees to open or close to allow the grey water out; in cases where the grey water tank is located underneath the motorhome without being winter insulated, you will quickly see the tank if you look under the motorhome and notice that a hose or pipe is going out from the tank to the side of the motorhome where you will see the drain valve.

If your motorhome is made for winter use and you have an insulated grey water system, you will typically not be able to see the grey tank underneath the motorhome; on some models, it will still be underneath but insulated and maybe with some defrosting cables inside the tank to prevent freezing.

More commonly, it will be located inside the motorhome, inside the double floor near the fresh water tank. In this case, the grey water drain valve will also be located inside the motorhome, usually in one of the storage places inside the double floor near a hatch.

Suppose you are draining the grey water tank after a trip and won’t use the motorhome, RV, or caravan for more than two weeks. In that case, it is also suggested that you drain the fresh water tank to make sure it won’t start growing algae or bacteria in the fresh water tank I have made another article about how to empty the fresh water tank as well as if it is safe to drink the water inside your motorhome or more importantly how to keep it safe to drink the water in your motorhome so I suggest you read those other articles as well.

If you want to learn where and how to find grey water disposal sites check out my video below!

Rikard Adamsson

Hello! My name is Rikard Adamsson; I am the creator of Motorhomeking.com. I live full-time in my motorhome, and right now, I am traveling through Europe the right way, without campsites; yes, wild camping and being off the grid works excellent even in a real beauty from 1996. I have done a lot of rebuilding and upgrades. I am happy to share my experiences with everything regarding motorhomes, RVs, or caravans with you here at motorhomeking.com.

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