What Happens When Grey Water Tank Is Full? (Overflow Damage)

Full is full. When the idiot light comes on, you should pay attention to it. Those lights are there to tell you that you should empty your gray water tank. If you don’t and your shower pan is not that deep, you can have a smelly and messy problem on your hands.

What happens when the grey water tank is full? If you are lucky, your shower pan will be deep enough also that no overflow damage will occur. However, if you are not lucky, then you can have a ruined carpet, lots of foul odors and possibly flooring damage if you do not catch it in time.

To learn more about overflowing gray tanks, just continue to read our article. It goes in-depth so that you have all the information you need to avoid this situation. Take a few minutes and get prepared for when it happens to you.

What Happens When The Grey Water Tank is Full?

For most RV designs, the gray water backs up into the shower. The reason it does that is because it is said that the RV shower is the lowest point in the vehicle or trailer. Once the gray water tank starts to back up you need to empty it as soon as possible.

When the gray water overflows, you won't have the really bad mess the black water tank makes but you will have a mess. The carpet will get wet, the cabinet bottoms, the flooring, and possibly the water will run out into the main part of the RV.

If you catch the overflow right away, the biggest issue you will have to face will be the odor. Other than that the water did not have enough time to do any real damage. But if there is a large gap between overflowing water and discovery, then you can end up with a lot more damage.

Water has a way of bringing mildew if it is left for a long time. That smell is hard to get rid of and sometimes you have to replace any carpet that got soaked. The cabinets may be more of an expensive fix if the water damage is thorough.

How do I Know When My Grey Water Tank is Full?


Most modern RVs will have sensors attached to the gray water and black water tanks. These sensors monitor your tank levels. Once the water reaches the full mark, a light on your control panel should appear letting you know that your gray water tank is full.

The other way to tell is to check your shower or sinks. If there is water in the bottom, then your tank is full and needing to be dumped. Also, if water does not go down your sink drain, then your gray water tank is full.

The problem with the sensors is that they are triggered long before the gray water tank is actually full. Some people have suggested that when your light appears, take a 5-gallon bucket, fill it with water and start pouring the liquid down your shower drain.

When you see water at the bottom of the shower pan, you now know where the actual full line is. It's an old-school trick but one that works every time. Sensors are not always accurate and they can malfunction at any time.

Some even indicate the tank is full when it is actually only half full. But if you want to be on the safe side, dump your tank when the light appears.

What do You do When Grey Water is Full?

Depending on how often you use the shower, the sinks, and your washing machine, your gray tank should be able to accept water between 1 and 3 days. That gives you a little time to get ready to dump the tank.

That is the most obvious answer to this question. When your tank is full, you unhook from the utilities and take your RV to the dump station. However, that is not the only answer and if you speak to many RV owners, they will let you know that they see no harm in keeping the gray water tank open while camping.

When they do that, they do not have to worry about the tank filling up. To them, they are not hurting the environment or anyone else as gray water is not as bacteria and germ-filled as black water.

Then, when they get ready to leave their site, they close the valve and let the tank fill up a little bit. That action gives them a little rinsing water when they go dump the black water tank. Those are about the only two options you have available as you have to get rid of the water somehow before it backs up into your trailer or RV.

RV Grey Water Tank Overflow


There is no real overflow system on most RVs. We cannot speak for every model but the ones we have investigated that system is absent. In a matter of speaking that is. There is no special overflow system that will hold the gray water in another tank underneath your RV.

The majority of RVs and trailers have an overflow system, though. Once the gray water tank is full, the water has to go somewhere. That location is the bottom of your shower. The reason the manufacturers use the shower as the overflow system is because it is the lowest point in your RV.

If you see water in your shower and it won’t go down, it is a big sign that your gray water tank is full. You will either need to open the drain valve and let some out, or go to the dump station and empty both the black and gray water tanks.

If by chance you see leaking water underneath your trailer or RV, then that is not evidence there is an overflow system in your model. It is evidence that there is a leak somewhere and that leak could be at your vent pipe junction.

The vent is too high to have any water leak out of it and the water would back up into your shower first.

Gray Water Tank Overflow Valve

There is a gray water drain valve but there is not a gray water overflow valve. The only valve connected to the gray water tank is the drain valve and that does not help when the tank gets full and starts to overflow. Unless you open it up and drain some of the water out.

The only exit gray water has is through your shower and sometimes through a sink. That is it. when you see the water rising, you need to take action right away so that the rising water does not damage your RV’s flooring, carpet, and cabinets.

There may be models that have 2 or three gray water tanks. These tanks will be connected to each other through valves and pipes but they are not really overflow valves. They are just extra tanks to give you more comfort when you camp for several days.

One tank can fill up in 2 or 3 days so having extra tanks lets you camp longer without dumping. But the shower remains as the overflow outlet and a sign you need to take action soon.

What Happens if You Overfill Your Gray Water Tank?


Generally, nothing will happen mechanically. The water does not reach any moving parts so it cannot ruin them. Unless you have a large flood and holes everywhere for the water to explore.

Electrically nothing should happen either although if your sensor did not light the full indicator light, you may have a problem with the sensor. Unless, of course, there is a frayed wire somewhere close to where the water happens to flow.

If your shower pan is deep enough and you can take immediate action to empty your gray water tank, then nothing should happen to your RV. The damage occurs when you do not notice the rising water and it happens to overflow when you are not around.

Then the amount of damage and how severe it is will depend on how long the water sits in one spot. Usually, the longest-lasting damage will be the odor the gray water causes when it soaks the rug.

Sometimes people get lucky as one owner found out that the water simply followed the edge of the carpet to the stairwell and flowed right out the door. Others are not so lucky and face a lot of water damage repair work. So the damage you face will depend on your RV’s position, level, and amount of water that is overflowing.

Grey Water Overflow Damage

This also depends as the water that is overflowing may not be coming up through your shower. There may be a leak somewhere that will cause a little damage to the insulation underneath your flooring.

Sometimes the junction between the air vent and the gray water tank can crack. This leaves a nice opening for the water to escape. If you are not fortunate, then you may see some damage to different parts underneath your RV including the insulation.

It is hard to say what will take place as every situation is different and it depends on how much water is leaking at the time. Loose valves are another source of overflowing water damage.

RV manufacturers are known to have loose connections between certain valves. To prevent this from being one source for your overflow problem, double-check to make sure the valves fit together and that they are tight.

Other damage will be inside your RV, not to your shower but to the flooring next to it. If you have a carpet or rug on the floor, the carpet or rug could be ruined. That is the worst-case scenario.

If the carpet is ruined, then it is possible that the flooring got damaged as well. But that usually takes a lot of water before the flooring gets ruined and needs replacing. The last place in the bathroom will be your particle board cabinets.

Particleboard is ruined if water gets to it.

When to Empty Grey Water Tank


This is subject to much debate. Not because people question when you should empty your gray water tank but if you should open the valve or leave it closed. You will need to have enough water in the gray water tank to rinse the black water tank but the gray water tank usually fills up first.

In that situation, you will be dumping your black water tank frequently if you leave the drain valve closed all the time. Since many RV owners feel that gray water does not harm the environment or the ground, they tend to leave their gray water drain tank open.

That means they only have to empty it once the black water tank is full. They only close the tank to give them enough water to rinse the black water one. To do this you would need permission from the campsite you are at or be way out in the forest where no one will see you leave your valve open.

Is it OK to Dump Grey Water On the Ground?

This will depend on the city, state, county, and campsite you are at. Each region and campsite will have its own rules as well as its own definition as to what constitutes gray water.

Arizona has one idea while Montana has another. The former state limits gray water dumping on the ground while Montana doesn’t want it done. Then you have those states and campgrounds that have decided that any water that comes in contact with food as black water.

Also, people are concerned about the soaps, shampoos, and other beauty products that land in the gray water tank. Those products can contain chemicals that harm the environment. The ph balance can be changed damaging the soil.

Then if you are camping near a stream, lake, or other bodies of water, it is best not to dump your gray water on the ground. The bacteria, etc., helps algae to grow, and that damages the marine life found in those waters.

If you take proper precautions, some states allow for gray water dumping. You would have to find the rules for each state you are going to visit and also ask the campground where you are going to stay to see if it is okay to dump your gray water on the ground.

Can I Leave My Grey Water Tank Open?


This is actually a continuation of the previous section. Every state and campground may be different. They all have their own rules concerning this topic and some RV owners do it despite what the rules and laws say.

We are not going to say it is okay because in some locations it is not okay to do this. Federal BLM lands have less strict rules and if you want to leave your gray tank valve open, then it might be a good idea to camp on those lands.

Part of the reason for the different rules is that some states consider gray water the same as black water. Your opinion may be different but that is the opinion that influences the rules of those states.

It is best to abide by the rules of the campsite and the state you are in when you go RVing. That way you will be welcomed back on your next visit.

Grey Water Tank Shows Full When Empty

This is a sensor problem that drives many RV owners to frustration. Sometimes the gauge will show empty when it is empty and then when a gallon of gray water enters the tank, the gauge flips to almost full.

One source for this issue is that the sensors got a little dirty. When that happens, the gauge will provide an inaccurate reading. One owner put a little detergent in their tank and let it slosh around as they drove. That solved the problem.

That was an easy solution and problem to diagnose. However, the sensor may be malfunctioning, have a loose wire or there is a short in the system. Those problems are a little harder to find and you will have to drag out your electrical tools or go to a qualified mechanic.

Some Final Words

Gray water tanks may become a thing of the past if most states have their way. By labeling water touched by food as black water, they might as well make the black water tank larger and eliminate the gray tank.

In the meantime, just keep an eye on your shower as that is a better indicator of when your tank is full than the gauges and sensors. When it starts to fill up, empty your gray tank.

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