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Old 03-09-2016, 08:50   #1
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Question Adding dip tube to holding tank?

This winter I'm planning on re-plumbing my holding tank as the hoses have permeated. I have zero clearance above, so all connections have to be on a side wall. I've been thinking about adding an elbow to the tank drain, with a vertical length of PVC pipe to avoid having sewage standing in the drain hose. I suspect this will limit the emptying of the tank, especially with the "macerator" (Sealand T12), so I was also looking at the commercial dip tube products. These require space above, which I simply don't have. As they're just pvc pipe, I could add an elbow internally. I didn't think much of the Dometic/Sealand installation though as there's no positive retention, just "Push the seal in the hole". However this might be the Uniseal that Peg Hall likes.

Is the Sealand dip tube worth the tank mod and hassle?
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Old 03-09-2016, 09:20   #2
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Re: Adding dip tube to holding tank?

The SeaLand does use the Uniseal...which you can buy direct from AussieGlobe (the mfr) The UNISEAL Warehouse - Home of the Original Uniseal for a fraction of the price SeaLand wants for their kit. It does not leak as long as there's no side-side stress pulling on it. The only fitting for which I won't recommend it is a waste tank discharge at the bottom of a tank, just to be on the safe side.

I think you're gonna need access to the inside of the tank to connect the pickup tube to the tank fitting, cuz the Uniseal is such a tight fit on the pipe that I don't think you can push it all the way to the bottom. But even if you could, how would you glue the pipe to the fitting?

Plan B: Instead of a diptube, aim your discharge elbow straight up and cement a piece of sched 80 pipe to the discharge fitting that reaches the top of the tank, then switch to hose the rest of the way to the pumpout fitting.

If you'd like to brain storm all this, send me an email.

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Old 03-09-2016, 12:07   #3
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Re: Adding dip tube to holding tank?

Quote:
Originally Posted by peghall View Post
...Instead of a diptube, aim your discharge elbow straight up and cement a piece of sched 80 pipe to the discharge fitting that reaches the top of the tank...
That will produce quite a lot of leverage against the discharge fitting/tank joint.
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Old 03-09-2016, 13:02   #4
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Re: Adding dip tube to holding tank?

It's worked on a lot of boats. The hose going up to the pumpout fitting should relieve any pressure on the tank discharge fitting. Any y-valve would have to be secured...overboard discharge pump would be installed after the y-valve, so neither of those would create any stress on the tank.
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Old 08-09-2016, 19:00   #5
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Re: Adding dip tube to holding tank?

Thanks for the answers. I realized after looking at the Uniseal instructions more closely that the seal needs to go in the tank first, and then the pipe in the seal. That (as you point out, Peggie) prevents inserting the dip tube with the elbow already glued in place.

My concern with the external pipe was that it would be more difficult to get the last 1 1/2" or so of waste out of the tank, but I think that it's actually no different from what I have now, with hose rising to the Y valve (which goes to the overboard pump and deck discharge). So that's what I'm going to do.

I hadn't thought about using Schedule 80, but as I'm planning on using pipe where I can (where I can allow movement to prevent cracking), the heavier the better.

I *still* haven't figured out the best way to vent--I have about a 4' rise from the top of the tank to the deck, and can only go aft from the tank in order for the vent hose to be hidden.
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Old 08-09-2016, 20:01   #6
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Re: Adding dip tube to holding tank?

If you'd like to brainstorm it a bit, send me an email.
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