How To Empty the Black and Gray Water Tanks

Are you the chosen one to connect the RV sewer hose, empty the holding tanks, flush the tanks and disconnect and store the sewer hose when it's time to leave?

Understanding how RV toilets are different from household toilets is the key to a successful outing in your travel trailer or motorhome. Knowing how to use RV safe tank treatments, and follow proper dumping procedures when it's time to empty the black tank is also important knowledge to be on your way to mastering your RV like a pro.

Let's get started:

For a better understanding of how this all works, I will start with some basics about the RV water system. The water system in your RV has many similarities to the water system in your house. They both need a source of potable water supplied to them. This water source in turn supplies water to the water heater, the kitchen sink, bathroom sink, shower, and toilet. In your house the wastewater that goes down the sink and shower drains, and the waste flushed down the toilet goes into a septic tank or a city sewer system.

Your RV has two wastewater holding tanks similar to a septic tank. The gray water tank collects wastewater from the sinks and shower, and the black water tank collects waste from the toilet. There is a monitor panel in the RV that lets you check the tank levels so you know when they need to be emptied.

I mentioned earlier, you need a source of potable water for your RV. Most campgrounds you stay at provide a potable water source to hook-up to. This is referred to as a city water connection. You simply connect a potable drinking water hose from the water source at the campground to the city water inlet on the RV and you have the potable water supplied throughout the RV.

Now let’s say that you want to get away from it all, you want to do some remote type camping where there is no water supply, better known as dry-camping or boondocking. Now what do we do for water? Sure, you want to get away from it all but no one said anything about not being able to take a shower. This is where your RV is unique; it has a fresh water holding tank that lets you carry potable water with you when a water source is not available. The capacity will vary, and can range from 10 to 20 gallons on a pop-up, and as much as 100 or more gallons in some larger RVs.

If you plan to travel or camp where a potable water source is not available, fill your fresh water holding tank through the fresh water fill, prior to leaving on your trip. The monitor panel lets you know how much water is in the fresh water holding tank.


In review, your RV has what is referred to as a gray water holding tank and a black water holding tank. The gray water holding tank collects dirty water from the kitchen sink, bathroom sink and shower. Some larger RVs have an additional gray water holding tank. The black water holding tank is for the toilet. These tanks terminate into one main outlet used to empty the holding tanks. This outlet is found somewhere on the outside of your travel trailer or motorhome, sometimes in a compartment. This is where we connect our sewer hose. The knife valves are usually labeled, but the small valve is for the gray water tank and the large valve is for the black water tank.

Make sure you have all the necessary couplings and connectors. It might be necessary to attach two drain hoses together to reach the sewer connection. I recommend you use heavy-duty sewer hoses. They are not that expensive and hold up better than cheaper drain hoses.

I recommend you keep a 10-foot and a 20-foot sewer drain hose available so you can always reach the campground sewer connection. You can purchase sewer drain hose kits with different length drain hoses and various connectors. Do not pull or drag the sewer hose on the ground, this can cause the hose to tear or get pin holes in it.

To connect the sewer hose, make sure both valves are closed and remove the sewer outlet cap. Make the connection by putting the drain hose adapter over the drain outlet and turn it clockwise until it locks securely in place. Take the opposite end of the drain hose over to the campground sewer connection. Use the necessary adapters and connectors to make the connection and get a good seal.

It may be necessary to use some type of sewer hose support to get a good angle from the RV to the campground sewer connection so the tanks drain properly when you empty them.

One golden rule for RV holding tanks is to never empty the black water tank until it is at least two-thirds full. You can check the tank levels at the monitor panel.

The tank should be close to full so the weight and gravity forces the contents in the tank to drain properly. Another golden rule is to never leave the black tank valve open at the campground and expect the toilet to drain or flush like the toilet in your home. It won’t work, and can lead to clogs and other problems you don't want. When the tanks are full, or nearly full always empty the black tank first, the large valve, followed by the gray tank, the smaller valve. The gray water tank should be at least two-thirds full too. Emptying the gray water tank last will help flush and rinse the sewer hose.

When you are at the campground for an extended period of time you can leave the gray tank valve partially open so it drains as you use it but remember to never do this with the black tank. If it’s time to leave the campground and your holding tanks aren’t full you can finish filling them with water and then empty the tanks. Add water through the toilet to finish filling the black tank, and add water through the sinks or shower to finish filling the gray tank.

Can I dump my black water tank if I do not have a sewer hook-up at my campsite or when I am traveling?

Note: Never let the gray or black water drain on the ground.

If your campsite does not have a sewer hook-up to drain your black water tank, ask at the campground office where their sewer dump station is located. You need to take your RV to the dump station to empty your black and gray tanks when needed. If you are traveling and you need to empty your gray or black water tank look for a dump station along the way. Some campgrounds offer this service for a fee (make sure you contact the office before going to the designated dump station). Some truck stops and fuel stations offer dump stations too.

Every time you empty the black water holding tank you need to treat it with a holding tank treatment to assist in controlling odors and to help breakdown solids. Always use environmentally safe holding tank treatments. Enzyme based chemicals use the good bacteria to digest waste and control odors.

The first step is to add enough water to completely cover the bottom of the holding tank. Four or five toilet bowls full of water should be enough, depending on the size of your black water holding tank. Water will assist a great deal in controlling holding tank odors. You always want the contents of the tank to be covered by water. Next, fill the toilet bowl with water and add the proper amount of holding tank treatment. Read the package directions. Flush the toilet. Repeat this procedure every time you empty the black water holding tank. Some holding tank treatments also contain valve lubricants to keep the valves operating properly and extend the valve seals life.

You should always use toilet paper designed for use in RVs. RV toilet paper breaks down and dissolves in the holding tank preventing potential problems with the holding tank, the RV sewer system and the dump station septic system. False holding tank readings on your monitor panel are caused by the holding tank probes, inside the tank, being covered by toilet tissue or other debris. To learn more about this read my article RV holding Tank Sensors and False Tank Level Readings

Note: When you work with waste evacuation and RV holding tanks it is a good idea to wear gloves. There are disposable gloves designed just for this. Check with your local RV camping supply store.

As a final note, it’s important that we do our part to make sure RV dump stations stay open and operational for the future of RV owners everywhere.

Here are five easy steps we can take to do our part

1) Use plenty of water in the black water holding tank.

2) Use enzyme based holding tank treatments rather than formaldehyde based chemicals.

3) Use only the amount of holding tank chemicals recommended for the size holding tank you have.

4) Practice good house keeping every time you use a dump station. Imagine if you are the person that has to clean up behind everybody else.

5) Never empty your holding tanks anywhere except in authorized dump stations and campground sewer systems.

RV holding tank sensors and false tank level readings, CLICK HERE to learn all about this subject.

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