We have a 2008 Newmar Canyon Star. Yesterday was our last day on the road home from Florida, so I wanted to empty the gray and black tanks. First I opened the black tank dump valve, and let it empty. I then opened the gray tank dump valve, and let it drain. Next I turned on the black tank flush valve, both dumps are open. While I was waiting for the black tank flush, I turned the fresh water intake valve to the "fill tank" position. I wanted to make sure we had at least half a tank of fresh water. After a few minutes, my wife came running out, yelling the bath room was flooding. I shut off both water hoses, and went in to find water all over the floor. The top drawer of the vanity was very wet. I could see water running down, what looked like a vent stack,( 2" black plastic pipe"). After I mopped up, everything seem normal. The water appeared to be clean, not gray water. I can't figure out what caused the flood. The fresh water tank was not over filled.

If you're sure that the black tank was empty when you turned on the flush valve, I'd think that the flush head inside the tank is aimed at the vent pipe. Sometimes the factory won't bother to weld the vent stack, or, they've been known to leave the vent stack with disconnected unions. Other then that idea, I'm at a loss of what might have happened.

The black tank may have been stopped up or the valve actually closed. Right after the incident you probably would have found the black tank to be full if you checked.

Atmospheric vacuum breaker. That's what's in your vanity. It's likely faulty.

Both dump valves were fully open. The black tank was only 1/4 full at the start, and the gray tank was full. The sprayer was only on a few minutes, and it was flowing freely in the dump hose. We have never had this problem before, so it may be the vacuum breaker, I forgot about that item. Thanks for the replys. I will be taking the coach in for service, before I put it up for sale. I want every thing in perfect working order, so a new owner won't have any regrets.

restorodder wrote:We have a 2008 Newmar Canyon Star. Yesterday was our last day on the road home from Florida, so I wanted to empty the gray and black tanks. First I opened the black tank dump valve, and let it empty. I then opened the gray tank dump valve, and let it drain. Next I turned on the black tank flush valve, both dumps are open. While I was waiting for the black tank flush, I turned the fresh water intake valve to the "fill tank" position. I wanted to make sure we had at least half a tank of fresh water. After a few minutes, my wife came running out, yelling the bath room was flooding. I shut off both water hoses, and went in to find water all over the floor. The top drawer of the vanity was very wet. I could see water running down, what looked like a vent stack,( 2" black plastic pipe"). After I mopped up, everything seem normal. The water appeared to be clean, not gray water. I can't figure out what caused the flood. The fresh water tank was not over filled.I never leave the gray water valve open when flushing the black tank, not that it should have backed up through there and blowing past your sink trap and you'd think with that being the case, it would come up through the sink drain as well. Anyway my procedure is to empty the black tank, pick up the hose to make sure it's clear. Close the dump valve for just a bit while turning the flush valve for filling. Then open the dump valve and letting it go while continuing some more with the flushing. Close both of those valves and open the gray which should have some water in it and hopefully some soap suds as well. A lot of this depends on whether or not you're staying or leaving and if you're just dumping or flushing the black tank. If just dumping, I like having some soapy water in the gray tank and like I said, open only one valve at a time, beginning with the black tank.

Bathroom flood - What did I do wrong? | Good Sam Community

Dutch_12078
Explorer II
May 06, 2013
dougrainer wrote:
Dutch_12078 wrote:
dougrainer wrote:
Dutch_12078 wrote:
Bathroom sinks are sometimes plumbed to drain into the black tank, likely to help balance the capacities. My last two motorhomes have been plumbed that way. The RVIA standards permit one device besides the toilet to drain into the black tank, but the shower is not normally used because of the higher backup risk.

The ONLY reason that any Gray source may go to a Black tank is because the floorplan design of the RV keeps that particular Gray source from going to the Gray tank. Doug

With all due respect, Doug, that's not always the case. The bathroom sink drain in my current Coachmen for instance, has an elbow that's just above the grey tank that directs the drain to the black tank about a 18" away. The drain could very easily, if not more easily, have gone straight into the gray tank.

I have been in the RV business 40 years. 5 building them and 34 as a tech. ALL Gray water will go to the Gray tank if it can. If it cannot, then they will plumb to the Black tank. That said, I HAVE over the years replumbed Gray from the Black because the factory plumbed a Gray to Black when there was adequate slope and a way to route to the Gray tank. But as I stated, IF the Gray can be routed to the gray tank, all will be routed there. Doug

I won't argue with your experience, Doug, but there are no signs that my Coachmen's drain plumbing has ever been modified from the factory installation. I actually do prefer having the bath sink go into the black tank though, since it helps balance the two tank capacities. My Allegro Bay, on the other hand, had been modified with a 3" connector pipe tying the two tanks together, making them functionally one large tank. I don't recall where the bath sink drained on that one, not that it made any difference.
tony_lee
Explorer
May 06, 2013
We'll all just have to wait until the OP gets back to us with the result of his investigations.
dougrainer
Nomad
May 06, 2013
Dutch_12078 wrote:
dougrainer wrote:
Dutch_12078 wrote:
Bathroom sinks are sometimes plumbed to drain into the black tank, likely to help balance the capacities. My last two motorhomes have been plumbed that way. The RVIA standards permit one device besides the toilet to drain into the black tank, but the shower is not normally used because of the higher backup risk.

The ONLY reason that any Gray source may go to a Black tank is because the floorplan design of the RV keeps that particular Gray source from going to the Gray tank. Doug

With all due respect, Doug, that's not always the case. The bathroom sink drain in my current Coachmen for instance, has an elbow that's just above the grey tank that directs the drain to the black tank about a 18" away. The drain could very easily, if not more easily, have gone straight into the gray tank.

I have been in the RV business 40 years. 5 building them and 34 as a tech. ALL Gray water will go to the Gray tank if it can. If it cannot, then they will plumb to the Black tank. That said, I HAVE over the years replumbed Gray from the Black because the factory plumbed a Gray to Black when there was adequate slope and a way to route to the Gray tank. But as I stated, IF the Gray can be routed to the gray tank, all will be routed there. Doug
Dutch_12078
Explorer II
May 06, 2013
dougrainer wrote:
Dutch_12078 wrote:
Bathroom sinks are sometimes plumbed to drain into the black tank, likely to help balance the capacities. My last two motorhomes have been plumbed that way. The RVIA standards permit one device besides the toilet to drain into the black tank, but the shower is not normally used because of the higher backup risk.

The ONLY reason that any Gray source may go to a Black tank is because the floorplan design of the RV keeps that particular Gray source from going to the Gray tank. Doug

With all due respect, Doug, that's not always the case. The bathroom sink drain in my current Coachmen for instance, has an elbow that's just above the grey tank that directs the drain to the black tank about a 18" away. The drain could very easily, if not more easily, have gone straight into the gray tank.
BillMFl
Explorer
May 06, 2013
Run a dehumidifier in the bathroom for a couple days. It will dry things out quickly.
tony_lee
Explorer
May 06, 2013
dougrainer wrote:
Your problem is the Vacuum Check valve for the Black Tank flush system. The OEM's install this check valve usually in the Lavy sink area. The valve is faulty and needs replaced. Connect the Black flush again. open the Lavy sink doors and have someone turn the water on and observe if you have water squirting out. That valve if leaking is the culprit. Doug

Tony Lee wrote:
I would check the black tank flush system. Mine goes from the hose inlet, up in the back of the vanity and then back down into the black tank. There is a vacuum breaker at the top of the loop. (this is nothing to do with the drain system from the vanity bowl.)

One of the fittings was loose and when I turning on the black flush, had water spraying up inside and running out through the floor openings behind the water panel

Easy to check - take all the drawers out and have someone watch as you turn the black flush on.

Sorry Doug - I didn't read all the posts, including yours, before posting my suggestion. You got in first.

I wouldn't mind betting we have the right answer. Either the valve itself or one of the fittings
BigRabbitMan
Explorer
May 06, 2013
In my coach, the kitchen sink goes into the black tank. This does a couple of things: It puts kitchen sink waste into the black tank, it puts additional water into the black tank for emptying and also balances the volume going into the two tanks.

I like it that way.
dougrainer
Nomad
May 06, 2013
Dutch_12078 wrote:
Bathroom sinks are sometimes plumbed to drain into the black tank, likely to help balance the capacities. My last two motorhomes have been plumbed that way. The RVIA standards permit one device besides the toilet to drain into the black tank, but the shower is not normally used because of the higher backup risk.

The ONLY reason that any Gray source may go to a Black tank is because the floorplan design of the RV keeps that particular Gray source from going to the Gray tank. Doug
Jim
Explorer
May 05, 2013
Empty tanks. An installed clear plastic union at the tank outlet would help. Open a tank valve, one at a time. Run the sink water, if it drains into the black tank, you'll get flow, and you'll know.
tropical36
Explorer
May 05, 2013
Dutch_12078 wrote:
Bathroom sinks are sometimes plumbed to drain into the black tank, likely to help balance the capacities. My last two motorhomes have been plumbed that way. The RVIA standards permit one device besides the toilet to drain into the black tank, but the shower is not normally used because of the higher backup risk.

Interesting and how does one find out where their bath sink is draining to?

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