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post #1 of Old 11-19-2012 Thread Starter
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Question Orientation of Flexible Holding Tank

Hello all:

The PO of my boat had purchased an Avon flexible holding tank, fittings, macerator pump, and hoses to bring the boat up to current standards (currently, all waste discharges to the ocean). I have decided to install these components since I have them, having to add only a Y valve and vented loops. I have read enough from those who have flexible holding tanks to be comfortable with its use.

My question is the positioning of the tank. It appears that they are designed to be installed lying flat, with the hose fittings at the top. If so, how does the waste exit the tank at pump out? I am new to boating and have never experienced a holding tank pump out or flexible tank. My RV discharges by gravity, so this is all new to me. Will the pump out create a suction that would keep the discharge fitting in contact with the waste? Does the fact that the tank is flexible necessitate that the top will always remain in contact with the discharge opening since the tank will naturally collapse as it empties?

Neither of the 1 1/2" fittings have a pipe that would protrude into the tank and reach down into the waste as I have seen diagrammed in top-fed discharge systems with rigid tanks. And, I don't think it would be wise to have the edge of a pipe coming into contact with the bottom of the tank when its empty, anyway. Also, it would seem the the tank vent, the center fitting of the bladder, would break any suction that pump out would create.

As always, your assistance with this matter would be greatly appreciated.


S/V "Spirit" - 1971 C&C 36R
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