Repurposing a Holding Tank for Waste?

J

JoLin

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My 1992 Carver. The fresh water tank is bigger than I need and the waste tank is too small. Would like to buy a smaller fresh water tank and use the current one for waste. I'll need to change some fittings, but there are relocation parts/kits available for that.

Both plastic tanks 'seem' to be made of the same material and thickness. Can one be substituted for the other?
 
They are both probably rotomolded polyethylene. If the fresh water tank is of the same thickness, it should work just fine.
 
Water might taste a bit funny out of that tank.
 
quote:
Originally posted by Anchor Management

Just switch the lines. Use you water for waste and your waste for water. :)

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How did I know that somebody would suggest that...

Thanks, guys.
 
Do you have room to work on the water tank because I'm thinking you will have some plumbing to do. I believe most holding tanks have a tube that goes to just short of the bottom for sucking out the shiz. My water tanks just dump into the top of the tank and exits out near the bottom on the other end.

Good luck
Niles
 
quote:
Originally posted by easttnboater

They are both probably rotomolded polyethylene. If the fresh water tank is of the same thickness, it should work just fine.

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Good point, too thin could collapse under the pressure of the suction.

Niles
 
quote:
Originally posted by nwaring

Do you have room to work on the water tank because I'm thinking you will have some plumbing to do. I believe most holding tanks have a tube that goes to just short of the bottom for sucking out the shiz. My water tanks just dump into the top of the tank and exits out near the bottom on the other end.

Good luck
Niles

Click to expand...


The 'suck out' for my black water tank is at the bottom of the tank, so no tube. Good point, tho. Yeah, there'll be some plumbing to do, and fittings to be changed.
 
The problem with the outlet being at the bottom of the tank is that you constantly have waste there where the fitting meets the tank and the hose meets the fitting. I had a leak there once with my old holding tank and it was not fun to clean up after. It also causes waste to always be sitting in a portion of the hose which makes it permeate faster. That fitting location also makes it more difficult to change hoses - you have to have the tank completely empty to do it.

So I will stick with the dip tube approach from here on out.

If you have access to the top of the proposed new tank, I think you could probably put in a dip tube and abandon (permanently seal) the fitting on the lower side. You probably have to do something with that outlet fitting, as I would think the outlet for a water tank would be small, like 3/4" and that's not going to work for waste.
 
The current black water tank has been without a pickup tube since 1992. I plan to change out hoses when I swap out the tank. That'll address the permeation issue. I think adding a tube is more work and complication than I need, but I'll look into it when I'm figuring out all the plumbing fittings I need to buy. If this doesn't work out and I end up buying a new tank I'll do the tube. Thanks for the tip.
 
Consider this then - look at having a portion of that hose that attaches to the lower fitting actually be PVC. You could couple it to the tank with one of those heavy black rubber coupling fittings they sell at HD. I did this with mine even though I have the dip tube, because the way mine makes its way up to the pump out fitting, it has to duck down and cut under some other things that are in the way and there are low spots I think waste sits in. Those areas are now PVC and presumably will outlast the boat, or me.

It was more work than just using hose, but it wasn't terrible.
 
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