The Correct Way To Dump Your RV Black Water Tank

By Steph | New To RVing

Apr 09

As a new RV owner, there are certain things that you must learn before hitting the road…like how to dump your rv’s tanks!

Many things about living in an RV are not that different from living in a “sticks & bricks” home. However, there are a few aspects of life on the road that are vastly different. Just like it is important to know how to care for a “regular” house, it is very important to know about the “inner workings” of your RV as well!


We are members of quite a few RV groups on social media and one of the things that I see people asking constantly is how to maintain their tanks. We see questions like, “should we leave tank valves open?”, “do you use tank chemicals and what kind is best?”, and the biggest mystery of all seems to be…”how do we dump our tanks?”

We are going to cover all of these questions and more in this blog post! Dumping your pee and poop is not the most fun thing to talk about, but alas, it is a necessary part of RV living. And if you’re new to RVing, it really isn’t that bad! Follow this guide and you will find that it’s actually quite easy to maintain your tanks in good working order, and without any stink!

Anatomy Of RV Sewer Tanks

Most every RV has at least one black water tank, and one gray water tank. Just for clarification’s sake, your black tank is the poo & pee tank that is connected to your toilet, and your gray tank is the tank that holds everything else like shower & sink water. They are both also called RV holding tanks.

(Yes, I felt it necessary to clarify that because some people really do not know the difference in their gray and black water…and that’s ok…that’s that we’re here for!)

How To Use Your Tanks

How you use your holding tanks depends on what your situation is at the moment. You may be on full hookups and be able to run water nonstop just like you would in a house. Or, you may be off in the middle of nowhere boondocking and need to rely on your tanks holding everything until you can dump them.

Here is how we operate depending on our hookup situation;

Full Hookups: We hook our sewer hose to the septic/sewer connection at the site, open our gray tank valves and operate our showers and sinks just like we would in a regular home. We always leave our black tank valves SHUT!

You do not want the dreaded “poo pyramid” forming in your black tank when it comes time to dump!

When on partial hookups or when we are dry camping/boondocking, we use our tanks until they need to be dumped, and then go dump them. Pretty simple. There are ways to save space in your tanks so they do not fill as fast, and we will talk about those in a separate post.

Valves Open OR Shut?

This question gets asked a lot! Heck, we asked the same thing when we first started RVing, so I’m going to let you in on the secrets of full time RVers. We have a strict routine when it comes to tanks…so here goes.

  • Secret #1… NEVER leave your black tank valve open! Here’s what happens…

    Your tanks sit on a slight slope. They are designed this way so that when your unit is level, the tanks will be able to drain out the end and into your sewer hose. Because of that slight slope, liquids roll downhill. But imagine if you left the valve at the bottom of the “hill” open. All the liquids would go downhill, and drain out, but the solids would stay put at the top. This creates what RVers refer to as a “poo pyramid.” The solids will then be stuck and can become VERY hard to remove.

    You do not want this.

    What you DO want, is tank valves shut and LOTS of water in your tank. The more water, the easier it will be when it comes time to dump for everything to flow out like it is supposed to!

    *We also do NOT put toilet paper in our black water tank. You can but we opt not to as it helps prevent clogs. 

    I know, it isn’t the most pleasant thing to discuss but hey, it’s a part of life

  • Secret #2… Your gray tank valves can be left OPEN! When you are connect to a sewer connection, you can leave your gray tank valves open and operate your shower and sinks as if you were in a regular home. The best part is that you don’t have to worry about filling a tank.
    HELLO long, hot showers!
    *If you are on partial hookups, or are dry camping/boondocking, this of course can not be done.

Tank Chemicals

This may come as a shock to some…we do not use RV tank chemicals. When we first got our RV, we were given a bag of tank chemical packs from the dealer. We tried them for the first few weeks of full time living and I kept battling unpleasant smells. I know many people use tank chemicals and claim that they work, but I have had more luck with the following method;

We purchase the large gallon size blue dish soap from Sam’s Club. After each dump, I add several gallons of water and about a cup of blue dish soap.


The soap, coupled with plenty of water has worked well.

Note: We also use the ice method for cleaning when we have longer travel days. For the ice method: purchase a large bag or two of ice. Put about a cup of blue dish soap and all the ice down your toilet. As you drive, the ice and soap with slosh and scrape around inside the tank. The chunks of ice will scrape off any stuck on residue, and the soap de-greases at the same time. As the ice melts, it will cause the sludge to become liquid enough to dump at your next stop. Give it a good tank flush and you’ll be set!

Dump Day

We have 5 people in our family and a 39 gallon black tank. We can go about 7 days before we need to dump. About a day before I know we need to dump, I go outside and CLOSE our gray tank valves. Over the next day, our gray tank(s) get a good amount of water in them. This is because when you dump the tanks, you want lots of water to flush out the hose.

When it is time to dump, make sure that your sewer hose is tightly connected to the sewer pipe. (Check out our list of MUST HAVE items for dump day!)
  • FIRST… pull your black tank valve handle.
    Let the black tank completely empty. This may sound gross, but we opted for a clear elbow on our hose
    (it’s THIS awesome thing!) so that we know when it has finished emptying.

  • SECOND… if you have a flush option on your RV, hook up the water hose to your flush line. We have a separate hose for this that we keep attached to a wye (get one HERE) at the water spigot.
    Turn on your water (with the black valve still open) and let it run until the water runs clear. This is another reason we have the clear elbow.
    If you do not have a flush, you can purchase a flushing wand HERE. This is used inside the RV in your toilet. It sends a high powered rinse down into the tank.
    I then close my black tank valve and let a little bit of water go into the tank from the flush before turning off the water. (Just a few seconds is enough) Remember, you always want plenty of water in the black tank to help keep solids from causing problems.
    Turn off the water.
    *We flush about every other time we dump. Some people do it about once a month when full-timing but we find that we get the best results if we do it more often.

  • THIRD… Close your black tank valve and open the gray tank handle(s). Wait to let all of the gray tank water empty. This flushes out any remaining water that came from the black tank that might be in the hose.
    Then, if you are on full hookups, it is OK to leave the gray valves OPEN. If you aren’t, then go ahead and make sure your valves are closed.

  • FOURTH… After I have dumped all the tanks, I go pour my cup of blue dish soap down the toilet. If this was a time that we didn’t flush, I will add about 4 toilet bowls bowls of water down the toilet with the soap.

And that’s it! We are now ready for our next road trip.

It really isn’t that difficult and becomes an easy routine after you’ve learned how to dump your tanks properly. It takes us about 15 minutes once a week to maintain our tanks in good working order with NO STINK!

---Make sure to check out the video to watch our entire rv dump process from start to finish.---

About the Author

Stephanie (Mom) is the crafty one. She puts up with everyone's nonsense with a smile...and a glass of wine.

  • Derek says:

    If you think of anything that we missed while dumping the black tanks, please leave a comment!!!

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