Why to keep your RV’s gray tank closed when hooked up



RV waste management expert Doug Swarts of Drainmaster.com explains why RVers should not only keep their black (sewer) tanks closed when hooked up in campgrounds, but their gray water tanks as well. Open both tanks to dump when they’re two-thirds full, but do not keep either open until then. You’ll be surprised to learn why the gray tanks (sink and shower) should be kept closed until it’s time to dump.



newest oldest most voted
Notify of
Les Brandt

Chuck, I subscribe to your blog and read it every Saturday. You do a really good job with it! Like any service, it is difficult to satisfy all the masses. I certainly understand the extra work it would take to provide a transcript on every video you do or have a link to in your blog. In the cases of videos, it would double. Not to mention, that the contributor would also have to provide a transcript. While I empathize that not everyone can be in a position to get the bandwidth or afford the extra data requirements, there comes… Read more »

edward stevens

I loved the article on the difference between 30 amp and 50 amp benefits. Is there a way I could speak to Mr. Mike Sokol or get in touch with him via a website or email? Thanks


I used to do my grey tank the way he recommends in the video. After overflowing the grey tank and getting water damage in 5 out of my 7 RVs over 32 years, I started leaving my grey tank open. One overflow is a big problem, and anything I can do to avoid another one is worth putting up with a few minor problems. Yeah, and tank gauges don’t work any better when you keep the grey tank closed. And P-Traps in an RV are the same as a P-Trap in a house, you need to pour some bleach down… Read more »


Dave ,
You should have put an alarm in your shower pan as that is where gray water will overflow from your Gray tank first.
I would think the simple solution would be to dump your Gray water every 2 days or so to insure you don’t overfill your Gray tank. A simple 24 hour timer at your entrance door would also help serve as a reminder.
BTW — Pouring Bleach down your drains kills the bacteria you need to break down the waste in your holding tanks. –Doug (at) drainmaster.com


That’s why I chose a tub with a shower–so I can keep my grey tank valve closed until needed. It would overflow in my tub if the tank got too full. I know how many showere I can take before needing to empty as I find gauges are not reliable.

Sandy M

Chuck, some of us with limited internet would love to hear your advice. The request for a written copy of the video is easy to do. Just type it in under the video on the page that has the video, or post it as a comment. You are a writer and probably a fast typist, and probably already have a written script of the video anyway. We are just requesting a little help for us low bandwidth types. Should only take a few minutes of your time. This time of year, a lot of us are out in the boonies… Read more »


I bought a fifth wheel new, but the tank gauges are, at best, approximate. I can flush the black and the gauge works exactly once, then reads permanently full until flushed again. How can I figure out how long to leave grey tanks closed, with a washer to boot, when I simply cannot trust the tank gauges?


First I would open the Gray tank when doing the clothes washing. The key to all this is to keep your Gray valve closed until the tank is 2/3rds full or thereabouts. Two people in an RV will get a feeling for how full the Gray tank is getting over time. The shower pan is where Gray water will surface first, and you can get a moisture sensing alarm, but I would get a 24 hour timer and dump the Gray when it goes off. –Doug (at) drainmaster.com

Keira B

Both of my RVs have p traps in the sink drains. They are plumbed the same way as our house is. The only difference between my RV and my house is the addition of the holding tank and the hose that can be disconnected. If critters could come up the sewer line to an RV, and make it trough the P trap, they could also come up into your house the same way. If anything it is more difficult for a bug or rodent to come up into an RV than a house. They would need to climb into the… Read more »


Keira, We have not heard of any bug or critter or fly for that matter getting through the P-traps into the living space of the coach itself. WE have heard a number of times about things getting into the Gray holding tank. Sewer flyies get into the Gray tank then go up the vent and back down into the Black (if the coach has only 1 roof vent) tank. Now the flies can enter the coach when you open the toilet valve. In one case that happened to the wife and when the tank “sociologist” cleaned the black tank he… Read more »

Glenn Fidler

don’t have access to unlimited wifi. can not watch video, should have the story in written form so people can read it.

Toby pup

Agreed. And some of us do not have ultra fast connection. Written is better. Why wait all day to watch a “talking head.”

Tommy Molnar

Prior to watching this video, I’d never given much thought to this. We generally leave our grey tank open – UNTIL NOW. This makes perfect sense to me. We would close our grey tank the day before we were going to leave a park so there would be water to wash out the hose after the black tank was emptied. We thought everything was cool. We’re smart RV’ers, or so we thought. After 20+ years of RV’ing, I’m not averse to learning something new, especially concerning yukky black and grey tanks. We’ll be visiting the “RV Proctologist” when we hit… Read more »