Waste tanks

craig r

Member
Jul 21, 2021
56
8
8
Cambria, California
We have been motorhomes for many years and are used to having a separate black and gray water tank. This has Always allowed us, when in a campground with hook ups, to leave the gray water valve open so that it doesn’t back up into the shower. Now I’m seeing some information that GMC motor homes may have only one tank for both gray and black water. Is this true?
 
Craig,
This is true of the GMC upfit only. Many of the others have separate black and gray tanks. So, you have to look at each, but if it is a GMC upfit, it will have the one only as far as I know.
The biggest other was Coachmen that did the Royale and Birchaven (23) but some were also done be Avion and a few others.
Matt
 
my 78' Royale Rear Bath has two tanks

it was suggested to convert to one tank since I need to replace the black tank, HOWEVER due to the plumbing/layout of the rear bath floor plan setup - the two tanks are separated by crossmembers - so I'll need to stick with two tanks

- I would much rather have one.
 
If you are a student (or was forced to be) of RV history, you would understand that at the time our coaches were designed, there was a huge push on to eliminate the possibility of surface discharge of gray water that so may
RVs were set up to do. This cause a lot of bad feelings. GM people decided to not have that issue at all.
It was the cramp ground industry plan at that time to push for FHU and 50 amp everywhere. Some even wanted phone and cable TV as a standard post. Too bad that all collapsed.
Matt
 
Yup, the GMC's are one tank. If you're at a campground connected to sewer the best bet is to leave the valve closed until the tank is almost full, then dump it all at once. That will help keep the 'solids' from piling up.
 
Well, we have owned five motorhomes over the years, three class C and two class A all with separate gray and black tanks. I suppose that if we do end up getting a GMC this is just something we will have to figure out. Thanks for all the answers and all the advice. Hope to see you all down the road.
 
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Well, we have owned five motorhomes over the years, three class C and two class A all with separate gray and black tanks. I suppose that if we do end up getting a GMC this is just something we will have to figure out. Thanks for all the answers and all the advice. Hope to see you all down the road.


Were the waste tanks in your past motorhomes only 5" deep? These don't have much depth to them, so keeping the contents as watery as possible helps with dumping.
 
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My single tank presents no problems, a few good long toilet flushes prior to/during dumping seems to work fine.

Larry
 
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Interestingly, our Coleman Popup camper (1988 Coleman Chesapeake) is 10 years newer than our '78 GMC. The popup has an inside galley sink (no bathroom) that just drains out onto the ground (factory setup). No gray water tank, no place to hook a sewer line, just a small rubber hose (with no fitting) sticking out under the camper.

The "gray" water is just like washing your hands outside at a hose spigot anyway.

(I know, just a pointless comment)
 
Interestingly, our Coleman Popup camper (1988 Coleman Chesapeake) is 10 years newer than our '78 GMC. The popup has an inside galley sink (no bathroom) that just drains out onto the ground (factory setup). No gray water tank, no place to hook a sewer line, just a small rubber hose (with no fitting) sticking out under the camper.

The "gray" water is just like washing your hands outside at a hose spigot anyway.

(I know, just a pointless comment)

I like that the grey water is combined into the black tank. Helps to keep the 'solids' flowing in a 5" deep tank. No depth to assist with the dump.
 
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O. K. We joined the cult. Just bought a 1974 coach. Not sure what model but it is super clean with a new motor,a “Manny tranny” and a 3.7 final drive. Guess we will have to figure out the holding tank issue now. Thanks for all the helpful reply’s. Hope to see you down the road.
What colour exterior and interior do you have?
 
O. K. We joined the cult. Just bought a 1974 coach. Not sure what model but it is super clean with a new motor,a “Manny tranny” and a 3.7 final drive. Guess we will have to figure out the holding tank issue now. Thanks for all the helpful reply’s. Hope to see you down the road.
I am going to go out on a limb…. Being a 74 it is only going to have the standard single black/grey tank combined. 75 was start of transmode and those where what you would find dual tanks on.

Tank capacity is an issue. No doubt.. but can be managed.