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Old 07-20-2017, 01:29 PM   #7
HeadMistress
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City: AR
Join Date: Jul 2009
Posts: 2,515


Get it all out of there, it will rust away and make a mess forever, plus life is too short to clean it.

I definitely agree with that!

... bottom discharges are less trouble than top but make sure if you use the bottom one that the hose slopes away from the tank so it will not hold poop and permeate rapidly.

But I definitely DISagree with that! A discharge line at the bottom of the tank to a deck pumpout fitting will fill with tank contents to the level in the tank. A line that slopes down from a discharge at the bottom of the tank eventually has to go up to the deck fitting...it'll fill with tank contents all the way to that turn and beyond. A "P-trap" in that discharge line MIGHT allow a bit more to be pumped out, but that's all it can do...meanwhile it will stay full of tank contents.

Otoh, putting all fittings on the top of the tank instead of on the side or end not only increases the number of flushes that the tank can hold, leaves no sewage standing in any line. A pickup tube inside the tank long enough to touch the bottom and cut diagonally about 25 degrees (any sharper leaves too much in the tank, flatter can trap undissolved solids and TP under it) leaves less in the tank than is possible from a discharge at the bottom no matter how it's plumbed. When fittings are on the top of tank that can also be dumped at sea, TWO discharge fittings--both with pickup tubes of course--eliminate the need for a y-valve in the discharge line.
However, 1.5" fittings need at least 5" clearance above the tank, which isn't always possible. In which case, the only good solution for a discharge fitting at the bottom of a tank is to run sch 80 PVC from the discharge fitting to the top of the tank, then switch to hose.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
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Specializing in marine sanitation since '87.
Author "The NEW Get Rid of Boat Odors"
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