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Old 03-02-2015, 07:22 PM   #1
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Vented loop or check valve for toilet discharge line

My aft head back-fills when the holding tank is full and the sea is rough. The current line from toilet to holding tank is straight. Holding tank is slightly higher than the toilet bowl (a retrograde installation). System can not discharge overboard. Why wouldn't just a check valve on the line near the holding tank prevent backwash rather than the more difficult task of putting in a vented loop?
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Old 03-02-2015, 09:02 PM   #2
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Every in-line check valve I have ever seen can potentially leak or clog when anything other than reasonably clean liquid is encountered. That is one of the reasons why they are not recommended on bilge pump discharge lines. Also, depending on the design, they can introduce additional resistance to overcome spring pressure or the shape of the interior.

Just some thoughts based on what I have read about check valves. Some may work better than others.
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Old 03-02-2015, 09:13 PM   #3
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A check valve is an obstruction in the discharge that will trap solid waste and TP and is and ideal location for mineral (sea water and fresh water) and urine crystal buildup. The second time you have to clear a blockage you'll decide to put the loop in the line and wish you'd done it in the first place.

Installing the loop isn't that bad a job, actually, if you put it immediately after the toilet...just switch out to a 90 discharge fitting if you don't already have one, rotate it to aim it up...mount the loop on the bulkhead behind the toilet and come down to connect with the rest of the discharge line. And you'll find the loop has an unexpected advantage: you'll only have to flush long enough to clear the top of the loop...gravity will take it the rest of the way to the tank. Switch to dry bowl (assuming that your toilet has that capabilty) to push some rinse water over the top and you'll reduce any run back to less than half a cup. Or don't...instead remove the joker valve and you'll have a bowl that can hold water "like the one at home."
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Old 03-02-2015, 10:08 PM   #4
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Yup, Peggy is correct. I have 3 vented head loops in my vessel. Two for the heads and one for the macerator pump.
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Old 03-02-2015, 10:18 PM   #5
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Quote:
Originally Posted by HeadMistress View Post

Installing the loop isn't that bad a job, actually, if you put it immediately after the toilet...just switch out to a 90 discharge fitting if you don't already have one, rotate it to aim it up...mount the loop on the bulkhead behind the toilet and come down to connect with the rest of the discharge line. And you'll find the loop has an unexpected advantage: you'll only have to flush long enough to clear the top of the loop...gravity will take it the rest of the way to the tank. Switch to dry bowl (assuming that your toilet has that capabilty) to push some rinse water over the top and you'll reduce any run back to less than half a cup. Or don't...instead remove the joker valve and you'll have a bowl that can hold water "like the one at home."
Yes, easy job if you're OK with the loop and hoses in plain sight. If you want the loop out of sight (under an adjacent vanity, for example) it's typically a major pain in the neck...but it can be done.

Gravity will only take all of the sewage flow from the loop to the tank if the line after the loop is down hill all the way. Some will still pool in an uphill discharge hose if you "come down to connect with the rest of the discharge line" (presumably at the original level of the pump discharge). But at least it wouldn't back into the bowl. I'd attempt to use the height advantage to reroute a rigid line directly to the exit from the loop.


Any water, clean or otherwise, that is in the column between the exit from the pump and the top of the loop will drain back when the pump stops. I'm not familiar with a dry flush feature, but don't believe it would preclude drain back into the bowl resulting from a loop installation. In my experience, joker valves invariably leak...so you'll have water in the bowl whether the valve is there or not. Take it out and the pumping action also improves. The installations in our boat (~24" of hose from the pump exit to the top of the loop...both located under adjacent vanities) result in a 5" diameter pool of water in the bowl of the old Raritan Crown. Never had a splash issue underway. I mounted the loop as high as possible (under the vanities) to achieve a constant gradient to the tank.

For our forward head I relocated the Y valve such that it sits directly under the exit from the loop. Super tight installation under the vanity counter top and next to the sink. But completely out of sight. Have to remove the drawer next to the sink to access the Y valve. The pollution police don't have a clue how it all works or even that it's there..
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Old 03-03-2015, 07:53 AM   #6
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"My aft head back-fills when the holding tank is full and the sea is rough."

A vented loop will do nothing for an overfilled tank flowing down hill into the toilet.

Replace the duck bill and the bowl will stay empty , but not for long.

I would rather work out an underway dump procedure for the full tank .
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Old 03-03-2015, 09:56 AM   #7
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"My aft head back-fills when the holding tank is full and the sea is rough."

A vented loop will do nothing for an overfilled tank flowing down hill into the toilet.

Replace the duck bill and the bowl will stay empty , but not for long.

I would rather work out an underway dump procedure for the full tank .
It will if the top of the loop is above the top of the tank, which is the objective/point. But as I stated earlier...the uphill portion of a line would still accumulate sewage. Using a properly positioned loop and taking advantage of the height to correct the gradiant of the line to the tank should also reduced the amount of water per flush and will obviously reduce odor. Joker valves are a joke. Don't get caught dumping on the Great Lakes...
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Old 03-03-2015, 10:32 AM   #8
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Two questions:
  • Does not a vacu flush design vs head located pressure pump alleviate this problem?
  • How about if your holding tank is too high, like under a bunk or somewhere (ours is below the toilet and pump level), won't that cause problems?
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Old 03-03-2015, 10:52 AM   #9
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Quote:
Originally Posted by sunchaser View Post
Two questions:
  • Does not a vacu flush design vs head located pressure pump alleviate this problem?
  • How about if your holding tank is too high, like under a bunk or somewhere (ours is below the toilet and pump level), won't that cause problems?
Sure, a vacu flush should block flow back. But they come with their own set of issues.

The OP stated that the inlet of his tank is indeed above the pump outlet, hence the problem when the tank is full and in rough seas.


By the way, I'm guessing that the vented loops on your boat are in the overboard discharge lines...different than this situation. Our OA had such loops whose purpose was to eliminate the chance for sea water to flow back into the head. I converted our aft head to be tank only (same as the OP's installation). And as I mentioned earlier I moved the Y valve for the forward head directly under the discharge from the relocated loop (they're virtually "stacked"). The net effect is that the loop serves two functions. First it protects from sea water incursion when the Y valve is in the over board position. Second, it provides the water in the bowl odor block, better pumping action (no joker), lower water usage per flush, and lower amp draw when the Y valve is in either position.
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