I would like to have more black water capacity, ...
...
It would be nice to be able to take 12 showers and still have the capacity to handle whatever cooking and washing needs to be done. ...

I would like to have more black water capacity, we use the coach as a tow vehicle for our play car, we autocross, hill climb and run track events with it and the GMC is the way to get there and the place to stay. None of the places we go have RV facilities and at most of the events we are the organizers so I don't have time to run out and find a place to dump. With the 24 Gallon waste tank it doesn't make it through a 4 day weekend without needing to be dumped. It also leaks when full so it needs to be replaced so I'm thinking of a bigger tank to help get us through the longer weekends.

It would be nice to be able to take 12 showers and still have the capacity to handle whatever cooking and washing needs to be done. That would be 4 people taking 1 shower a day for 3 days.

Has anybody found a large tank that will fit the GMC frame? Filling the space the small tank is in now would be around 50 Gallons which would work good for us.

If that is to much weight to pack around there are dump sites fairly close on most of our venues so I could dump on the way out.

Thoughts?

24 gallons sounds small. Where did you get that number?

And 4 people using the toilet, too.

I'd be tempted to figure out how to install a gray water tank and plumb
the shower and sinks into that. My PO actually built one from 4" PCV
pipe that fits under the bed but it only drains the sinks, not the
shower. If you could get a gray water tank under the floor you could
plumb the shower into it.

Also an option to use an external gray water tank that could be dumped
(at night when nobody is looking) in the woods or into a manhole cover.
Not that I'd advise that, ever...

I think your black water tank is larger than 24 gallons, though.
Probably not 12 showers and 4 people worth, though.

Kelvin
'73 23' in Eugene, OR
Who doesn't autocross or hillclimb anymore.

My 73 Operating Manual says the OEM holding tank was 40 gallons. Why is yours 24? If you are going to replace it, get a 40 gallon one. Also, stop taking showers and start taking bird baths. Why do Americans look for ways to waste everything? Learn how to cut back. My CFO runs the water while brushing her teeth, so the kids do too. What's up with that?

someone at GMCMI convention, built a plywood/epoxy type of extra capacity holding tank. I wish I had a chance to see it.

I have a similar issue with not enough black tank capacity, because I camp with 2 daughters and my wife. I installed a new GMC 1 tank this spring, and without testing, I think there is less capacity, even though it fit like original. but maybe because my kids are a year older, they are using more water?

Anyhow, here are my suggestions to you... 1st, pull the tank and check it out.. see where your leak is, and maybe you can repair that, so it does not leak when full. However, it might be better for it to leak out under the coach when it is full, rather then over flow into the shower if it fills up.

my other suggestions are as follows:
1. hole saw another drain into the shower, and plum it of to the side so it either drains off to the ground, or you can maybe hook a hose to drain it to wherever. and when you are showering in location where you can just have the water hit the ground, do so. that should allow more showers. but some places and people frown on that practice.

2. install one of these:
http://www.amazon.com/Thetford-Exterior-Shower-Box-Head/dp/B002UC10ZA/ref=sr_1_12?ie=UTF8&qid=1412299388&sr=8-12&keywords=rv+outside+showe r

and buy one of these:
http://www.amazon.com/Stansport-Cabana-Privacy-Shelter-Green/dp/B0006V2B4G/ref=sr_1_1?ie=UTF8&qid=1412299482&sr=8-1&keywords=outside+showe r+tent

then just shower outside, water hits the ground.

other suggestion, would be with a macerator installation, build a holding tank into your trailer for your car. and then you can easily pump the water from the GMC to the holding tank on the trailer.

Also an option to use an external gray water tank that could be dumped
(at night when nobody is looking) in the woods or into a manhole cover.
Not that I'd advise that, ever...



Please try the woods.. do not dump into manholes... I have to work in those occasionally.

I would like to have more black water capacity, we use the coach as a tow vehicle for our play car, we autocross, hill climb and run track events with it and the GMC is the way to get there and the place to stay. None of the places we go have RV facilities and at most of the events we are the organizers so I don't have time to run out and find a place to dump. With the 24 Gallon waste tank it doesn't make it through a 4 day weekend without needing to be dumped. It also leaks when full so it needs to be replaced so I'm thinking of a bigger tank to help get us through the longer weekends.

It would be nice to be able to take 12 showers and still have the capacity to handle whatever cooking and washing needs to be done. That would be 4 people taking 1 shower a day for 3 days.

Has anybody found a large tank that will fit the GMC frame? Filling the space the small tank is in now would be around 50 Gallons which would work good for us.

If that is to much weight to pack around there are dump sites fairly close on most of our venues so I could dump on the way out.

Thoughts?

...The black tank measures out to be about 30 gal max (no way the OEM tank can be 40 gal) ...

Adrien G. wrote on Thu, 02 October 2014 22:10

...The black tank measures out to be about 30 gal max (no way the OEM tank can be 40 gal) ...

Operating Manual X-7321A, © General Motors Corporation, Page 120:

"Living Area Water Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Gal.
Holding Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 Gal."

Could be a misprint. Could be an exaggeration. I dunno, but the manual says 40 gallons. The Operating Manual FOR YOUR 1975 model says it came with a 32 gallon holding tank (and a 40 gallon fresh water tank - talk about a problem waiting to happen). The standard GMC waste tank Jim K. sells is 30 gallons.

I would like to have more black water capacity, we use the coach as a tow vehicle for our play car, we autocross, hill climb and run track events with it and the GMC is the way to get there and the place to stay. None of the places we go have RV facilities and at most of the events we are the organizers so I don't have time to run out and find a place to dump. With the 24 Gallon waste tank it doesn't make it through a 4 day weekend without needing to be dumped. It also leaks when full so it needs to be replaced so I'm thinking of a bigger tank to help get us through the longer weekends.

It would be nice to be able to take 12 showers and still have the capacity to handle whatever cooking and washing needs to be done. That would be 4 people taking 1 shower a day for 3 days.

Has anybody found a large tank that will fit the GMC frame? Filling the space the small tank is in now would be around 50 Gallons which would work good for us.

If that is to much weight to pack around there are dump sites fairly close on most of our venues so I could dump on the way out.

Thoughts?

Bpimm,,, I didn't like the grey tank being full after 2 days of dry camping. Soooo,,,, I installed a 50 gal grey and a 40 gal black tank. Can't remember who I got the tanks from but they have a huge seleltion. But,,, it makes the bottom of the tank relly low. At the International rallys I dump when i leave and never travel far with these full. I'll look at my old posts and search my records. Maybe????