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Old 16-04-2011, 17:12   #1
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Holding Tank Draw Pipe

Hi folks. I'm doing a new holding tank, to be emptied via a draw tube from a fitting on top. I'm using 1-1/2" ABS for the draw pipe, through a Uniseal.

My question is about the bottom of the draw pipe. I know it needs an angled cut so that it can suck up the... chunks... but I'm not sure how big an angle makes sense. For now I've cut it to just under 45 degrees, which gives about a 1" clearance to the highest edge. That will leave 1" of water / waste in the tank at all times, which I'd rather not have (though the tank's at a bit of an angle, with the draw pipe at the bottom edge, so it won't be the whole tank).

Does it sound like that's the best plan? Do you think 1" is enough? (I'm using a manual toilet and no macerator.) Could I get away with less?

Thanks for any opinions!


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Old 16-04-2011, 18:19   #2
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Re: Holding Tank Draw Pipe

Take a look at this part from Trionic (Holding Tank Pump Out Kit). What they've done is put in a elbow (not sure the angle) to turn the pipe, then cut it off so it is parallel to the bottom of the tank, about half an inch off of the bottom.

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Old 16-04-2011, 18:38   #3
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Re: Holding Tank Draw Pipe

Standard discharge size is 1.5" hose...that's the size that will fit the barb on the deck pumpout fitting and also the size of the inlet fitting on a macerator pump...and the size of both the inlet and outlet on most manual diaphragm waste pumps.

So you'll need a piece of pipe that has a 1.5" OD (OUTER diameter), which will prob'ly mean it'll have a 1.25" ID (INNER diameter). Best to take a piece of hose with you to buy the pipe to be sure. The pipe should touch the bottom, cut at about a 25 degree angle. That will leave only a little more than 1/2 in the tank.

Btw...SeaLand/Dometic also makes a kit for this, but I can't see spending upwards of $25 USD inlcuding shipping for something you can easily make for <$10.

No need to worry about whether the pumpout can "suck up the 'chunks'"...there won't be any. Solid waste is at least 75% water...gets broken up by the toilet dissolves in water very quickly.

You MAY be required to use a macerator pump to dump the tank. I say "may" because I know that Queensland marine sanitation regs require that waste from a vessel within 1 mile of shore be macerated, but not sure where else in OZ that may be true.
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Old 16-04-2011, 20:00   #4
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Re: Holding Tank Draw Pipe

Thanks Jay and Peggie! The chandlery I bought the tank from offered me a 'kit' too... using basically a uniseal (but different brand I think), and some PVC with a 45 elbow similar to the Tiptronic setup. For $45.

The uniseal was $2.40 (I splurged and bought two, to have a spare), plus ~$5 of plumbing bits. I used 1-1/2 ABS, a 90 degree elbow on top, a female thread adapter and a threaded hose barb for 1-1/2" hose. It all seems like it'll work.

That's 2 votes for 1/2" clearance, so I'll recut the pipe at a reduced angle. Thanks for your assurances, Peggy; I've been worrying about solid chunks (e.g. I bought a wide radius elbow), apparently I don't have to.

BTW, I'm in Sidney, BC, Canada, not Sydney Oz. No pesky regulations about macerators and such here... until I cross the border to the San Juans.

Thanks folks!
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