Forum Discussion

Talisman61's avatar
Talisman61
Explorer
Feb 19, 2018

Single waste holding tank

While I'm working on a TC, I figured those of you in here would be better suited to answer this question.

I'm adding holding tanks to my $500 TC that has become a budget minded build. Not out of necessity, but because she's a 1971 unit that I'm not sure how much life is left in her.

Anyways, I need a black tank, and should probably add a gray tank as it's illegal to dump gray to ground.

Can I use a single tank for gray and black? I have a few reasons why this would be far simpler than 2.

1. The plumbing on this camper was originally designed to go to ground, so I dont have much room under it for pipes. with the kitchen sink on one side, and the shower,bathroom on the other with the toilet, it'd be nice to drop straight down after the traps to the tank rather than plumb together then to a tank.

In order to get both sides connected, I'd have to have piping below the top of the tank, not ideal.

2. Cost, one big enough to hold both gray and black is actually quite cheaper than 2 smaller ones considering the space I have to work with. I only have ~6" of height to accommodate a tank.

The downsides are what I'm coming to you guys for.

I see concerns with flushing when dumping, any smells will possibly come up the sinks if a vent has issues, and sloshing while travelling.

I have a 45" wide, 45" long, 6" tall space to work with if you have suggestions.

Sorry for the long post!
TIA!

28 Replies

  • Ron3rd's avatar
    Ron3rd
    Explorer III
    YES! You can use a single tank for the black and gray; new trailer manufacturers are already doing it, mostly as a cost-saving measure. Not ideal IMO but it is done.
  • Talisman61 wrote:
    Still don't see too much justification in there for 2 tanks,
    Then in your case it depends on how often you want to have to dump. A single will obviously shorten that time. If you ever use a blue boy, black is more unpleasant to deal with.
  • It is generally not a good idea because of potential over fill and back up. In your case it sounds like, it is not so much a question of can you as it is do you have another choice?

    We easily use three times more gray water than the black water. But if you really only have room for one tank there is not much choice. How many sewer lines do you have at home?

    If you have ever over filled a gray tank you discover it backs up into the lowest point. In our case it backs up into our TT's shower tub. I would not want that back up to be from the black tank.

    My PUP was no black tank and gray water empties to the ground or a container.

    If I installed a toilet and single tank, it would back up into the toilet before it would reach the sink height. Still not a good option.

    You could opt for a cassette toilet, or a portable black tank. We bought small Coleman camp toilette for a night time pee pot in the PUP. But, more often than not we take the TT.

    Good luck
  • For many years RVs (not just TCs) came with ONE waste tank

    Grey waste can be nastier then black due to rotten food, greases/oils/sloughed body skin etc

    Combine them and move on.

    Smells inside RV just means a 'vapor barrier' needs fixed.....dry 'P' trap, bad toilet bowl or floor flange seals, vents etc
    Odors inside...find fix problem vapor barrier
  • Instal a black tank and buy yourself a tote tank to handle the gray water. Otherwise instal two tanks.
  • 2oldman wrote:
    Why separate gray and black tanks


    Still don't see too much justification in there for 2 tanks, besides the shower overflowing issue. With only 2 of us, and a 25 gallon fresh water tank, we aren't going to be overflowing a 20 gallon waste tank in a few days. *I think*.

    I'm still looking for a decent priced "L" shape tank, regardless.
  • Should also be noted this camper will probably never see more than a 4 day outing.