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  #1  
Old 07-01-2003
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Head and vented loop

I am about to overhaul my marine toilet and it looks like that I have to add a vented loop between the toilet discharge and the holding tank. Does this mean the 3 feet from the toilet to the top of the vented loop is always full of waste? Can a marine toilet pump air until the hose is emptied?
Thanks, Markus
R29, Alameda
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Old 07-02-2003
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Head and vented loop

The vented loop goes on the sea water intake to prevent siphoning sea water into your tank or head. The Joker valve prevents backflow from the tank.
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Old 07-02-2003
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Head and vented loop

I just did that job last year. I repeated the installation the same way the original manufacturer did which was to install a loop vent at the outflow of the head. The outflow of the loop leads to a Y valve that can divert the waste overboard or to the tank.

This means that I have to pump the head about 10 extra strokes to push the waste beyond the loop. I think the hose is too great in diameter to move it through by pumping air alone. As a result, my tank fills up sooner than necessary.

It would make more sense to direct the waste to the Y valve first and divert the waste either into the loop for overboard discharge or directly into the tank. I think the problem might be that I run the risk of backflow directly from the tank if there is no loop to prevent it.

Both Boat/US and West marine equipment catalogs show diagrams of how best to install a new head. I used the odor-proof Trident hose. Soften it in boiling water before trying to attach it to make it easier.

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Old 07-02-2003
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Head and vented loop

foxglove, so you are pumping raw water until the waste is in the holding tank? Then you have always raw water in the upwards hose?
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Old 07-10-2003
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Head and vented loop

I can understand the vent on the intake water flow to prevent flooding in the head. But with a holding tank arrangement, it seems improbable to me that a siphon could develop between the tank and the head.

If one were using a direct overboard discharge, then siphoning could be a problem. I would expect that most boats with a holding tank would use the tank and then discharge overboard when full and legal. The overboard discharge line seacock should be closed except when emptying the holding tank. Am I missing something here?

Jim
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