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Re: [GMCnet] Need plumbing advice, please? [message #328520 is a reply to message #328518] Mon, 22 January 2018 20:11 Go to previous messageGo to next message
James Hupy is currently offline  James Hupy   United States
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Registered: May 2010
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Most of the Royale GMC'S I have worked on with two tanks, use the kitchen
sink draining into the Greywater tank, and the lavatory sink, shower, and
toilet draining into the blackwater tank. The two tanks have separate drain
valves, whose drain pipes join downstream from the valve. Without some
errors in plumbing, I don't see how water poured into the kitchen sink
would wind up in the shower drain, which dumps directly into the black tank
after the p or j trap.
Jim Hupy

On Jan 22, 2018 5:47 PM, "Ken Henderson" wrote:

> Justin, et al,
> I don't see how venting can possibly be the problem. To run into the
> shower pan, there MUST be liquid up to that level. H20 being a bit heavier
> than air, even if the tank had no vent (which it apparently now has two of,
> the original and the newly added one), the water would STILL go to the
> bottom of the tank, not up into the shower. Admittedly increased pressure
> in the tank MIGHT force a little bit, maybe a cup full, of water out of the
> P-trap, but no more.
> Ken H.
> On Mon, Jan 22, 2018 at 7:46 PM, Justin Brady wrote:
>> My guess is tank venting as well.
>> The water displaces the air in the tank, if the air can't escape the
> water
>> can't get in.
>> Most tanks have at least one vent straight to atmosphere through the
> roof.
>> Not sure of the grey setup on your coach though as I don't have a grey
>> tank!
>> --
>> Justin Brady
>> 1976 Palm Beach 455
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Re: Need plumbing advice, please? [message #328537 is a reply to message #328427] Tue, 23 January 2018 09:58 Go to previous messageGo to next message
kingd is currently offline  kingd   Canada
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Registered: June 2004
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Senior Member
I'm not a GMCMH owner but I've been follong the Forum (on-line version for many years)
I note your coach is a "Coachman". Do you know if it has one holding tank or two ?
If it has 2, the sink and the shower probably go to the same tank.

Is the black tank for the toilet directly under the toilet like on GM up fitted coaches ?
If it has 2 tanks are you sure you dumped both?
As someone has said, you may have pulled the handle, but it's possible the valve
didn't actually open and the tank is not empty. Can you check that?

DAVE KING lurker, wannabe Toronto, Ontario, Canada
Re: Need plumbing advice, please? [message #328546 is a reply to message #328537] Tue, 23 January 2018 14:50 Go to previous message
GMC Jimmy is currently offline  GMC Jimmy   Canada
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Registered: September 2016
Location: Niagara, Ontario
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Senior Member
Thanks for the ideas and suggestions fellows.

Initially my thought was a venting issue but after adding the second vent pipe didn't resolve the water backing up into the shower I wondered if it had something to do with direct venting to the atmosphere.

Ken H indicates that venting isn't the likely cause of my problem although it may cause a small amount of water not the amount I'm experiencing. So I need to look at other options like snaking the drains again in case it is a blockage of some type.

James, I'm quite certain I have two tanks and the main drain pipe services the lounge sink, bathroom sink and the shower.

Dave, I believe I have two tanks & two drain valves (one for each tank). Last summer, assuming the tanks were empty, (the fellow who did my per-purchase inspection confirmed both tanks were empty) I decided to run water into both the grey tank via the lounge & bathroom sink as well as the black tank via the toilet. When I pulled 1st the black dump valve I got what I expected, very little liquid. The same with the grey tank, only what limited amounts of water I ran through appeared to exit via the main dump pipe.

You could clearly see the result of opening each valve. Maybe I need to repeat this exercise, fill my water tank and empty 50% of it into each tank then empty each tank separately to try and identify the amount of water exiting.

The toilet appears to dump directly into the black tank and it looks like the main drain pipe connects the lounge, bathroom and shower. I will try and get some links to photos for you to look at.

In the meantime here is a quick schematic I just drew up giving you an idea of my set up...

Thanks again,
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