How To Position RV Dump Valves

It’s an age-old question in RV life. Which position are my dump valves supposed to be on full hookup? Which one open, which one closed? And some people just assume. Assuming the wrong way at times. So, let’s look at the situation and find the proper RV dump valve positions for full hookup.

A Story About Dump Valves

Back in March while we were in Florida for the Full Time Families, Family Reunion Rally. A family parked next to us with a brand-new trailer, they were just camping for a couple of days and not part to the rally. Well, I happened to notice his dump vales after he hooked up. The gentleman had opened both the gray and black water dump valves. Being a good neighbor, when I saw the man outside, I spoke to him about his mistake. 

I explained to him that he needed to keep his black water tank closed. That it should only be opened right before they left, or the tank gets full. The gray tank, on the other hand, can be left open. The man and I spoke for a few minutes then went on our ways. I now wish I could have that conversation again. 

If I Could Turn Back Time

Not that I believe I was wrong about which tank needs to be opened and which needs to be closed. That is how I leave my valves after all. But I wish I had thought to go in more detail about dumping tanks and rinsing them. What I failed to explain or give advice on is something that I try to remember to do the day before leaving a campground. That is to close the gray tank valve and let it fill that evening. So, after you dump the black tank you then dump the gray to wash out the dump hose. And to maybe even rinse the sewer hose out with a water hose also. 

You Need A Good Rinse

Another thing I wish I had mentioned was tank rinsing. Many RVs come with a tank rinser installed in the black tank. I actually installed one myself in The Tin Can. But a lot of people use the tank rinser that attaches to the dump valve opening. Where it blasts water back up into the tank. This tank rinsing is good to do periodically and really good to do if your RV is not going to be used for a while. 

Gray Tank Debate

Going back to the gray tank, some people may say that you should leave it closed even on full hookup. I’ve heard of people getting flies in their gray tank and having them come in their RVs. That’s pretty gross! I have yet to have that happen and as I stated earlier I always leave mine open. I tend to think that the fly problem most likely happens when the sewer hose is not properly “sealed” at the hookup. Allowing flies to go up the hose into the tank. I could be wrong. On my sewer hose, I have one of the threaded ends that I partially screw into the hookup fitting. I don’t tighten it up just a few turns, so it doesn’t come loose. I’ve also heard of sewer hose fittings that have a tapered rubber end that seals at the hookup fitting. Either will work. This hopefully will prevent flies and unwanted guest from entering your dump tanks.

My Two Cents

To sum it up, my advice on RV dump valve position while on full hookup is. The gray tank open and the black tank closed. Close off the gray a little while before dumping the black to chase out the black water in the hose. And having a tank rinser of some sort to help clean out the black tank. That is how I do my tanks and have had few problems. Your mileage may vary.

Please Like and Share us on social media! Also, subscribe to our email list to stay up to date on new posts! Please leave a comment telling us what you think.