The Definitive Guide to Using Your RV Waste Water Valves

March 02, 2020

Using Your RV Waste Water Valves Black Gray Tank Open Closed Avoid Clogs Odors in RV Motorhome Trailer Boat

Updated: March 2020

You've probably heard a dozen different opinions on how to use the gray and black tank valves on your RV. Should you leave them open or closed? Does it really matter? 

In this article, we'll walk through how your tank valves work and what part they play in proper waste water care. Using your valves incorrectly can lead to frustrating and expensive problems, so the better you understand how to correctly use your valves, the better your life will be!

Many RV owners understand that their tank valves play a crucial role in solving odor problems, preventing clogs, and ensuring that sensors continue to operate correctly. Unfortunately, there is a lot of confusion around the subject of waste valves, which explains why there are so many different opinions on how to use your waste water tanks. At the end of the day, we want to give you the resources to allow you to focus on the important part of your RVing experience: having fun and not dealing with holding tanks! 

Black Tank Valve Use

When it comes to your black tank, there is only one rule: ALWAYS KEEP YOUR BLACK TANK VALVE CLOSED

Your black tank valve should always be closed no matter what, except for when you are dumping your tank. This is really not up for debate. It might seem counterintuitive to contain your waste until you need to dump, but RV plumbing is a completely different beast than your home’s plumbing. 

By keeping your tank closed, you’re capturing all the liquids and solids that go into your holding tank until you need to dump. Those liquids are crucial to making sure you don't have solid waste drying out and caking up inside your holding tank, plumbing, and sensors. By keeping the liquid and solid waste contained until you dump, you are also able to use a high-quality RV toilet treatment to break down all of the waste.

Important note: If you leave your black water tank open, all of the liquids will trickle out into the sewer, and all of the solid waste will begin to pile up inside your tank, creating a pyramid plug—literally a "poop pyramid" of waste! Eventually, this pyramid of poop will grow high enough to block your toilet, and you will start getting toilet backups into your RV. Trust us, you don't want this to happen!

Remember: Dumping your tank is the only time that your black tank valve should ever be opened.

Gray Tank Valve Use

Using your Gray Tank can be a little more nuanced. When you are dry camping (or boondocking), it is also super important that you keep your gray tank closed

When you are on full hookups, however, we recommend you leave it open. 

Here's why…

Dry Camping

You must keep your gray valve closed when you dry camp. This is because dumping a large amount of used water is prohibited on public lands (i.e. National Forests, National Parks, Campgrounds, etc.). It is not a good idea to dump large volumes of wastewater, because it can contaminate local watersheds and attract insects and animals, which is why it is strictly prohibited almost everywhere. Beyond being illegal, dumping on public lands also goes against the very idea of “leave no trace.”

In many of these places, full hook up camping is not as readily available, so it is important to always keep your gray tank valve closed until you have access to full hookups or a dump site.

Full Hookups

If you have access to full hook ups, we recommend leaving your gray tank valve open.

Grease buildup inside gray tanks is a tough problem to clean up, and by keeping your gray tank valve closed, you will allow water to accumulate in your tanks. If suspended by water, grease—normally from food waste, soap, and dishes—will cling to your tank walls and start causing sensor issues and foul odors. By keeping your gray tank open, the water will naturally trickle out, which isn't a problem on full hookups, because there shouldn't be any solid waste to create a "pyramid plug" in your tank. 

Important note: Make sure you use sink strainers to keep food waste and debris from going down the drain into your gray tank.

Make a kink in your waste hose to prevent sewer smells from coming back into your RV

When leaving your gray tank valve open, we recommend making a P-trap in the hose running to the sewer. This will create a water barrier that will prevent sewer gasses from backing up into your RV. Please note that in some states, your waste hose cannot touch the ground, so please make sure you follow all local laws and ordinances.


There are many people who have tips or tricks to your valve use, but it really isn't rocket science. There are only a few simple rules: Always keep your black tank valve closed. No exceptions. With your gray tank, keep your valve closed unless you are on full hookups. By following these steps, you can be clog and odor free without the headache of constant maintenance and problems.

If you have any questions regarding any of the material we covered in this article, please reach out! We talk to hundreds of customers every day and would be happy to answer any questions you have. Email us here.

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