[src]

When you are cruising, water is flowing past the thru-hull fitting. Depending on the location of the thru-hull, this will produce either a high pressure (water trying to come in) or low pressure (water trying to go out) zone around the thru-hull. Think about driving the car with a window cracked open just a bit.

Due to the flow of water around the boat's bottom, I would suspect it is creating a low-pressure zone, which would tend to pull water out of your holding tank, even if the lines ran above the tank. Suction can pull water uphill, and it might even pull it through the macerator, depending on how that is constructed.

Also, if the tank is mounted higher than the water level outside the boat, once the hose is full you can still get a siphon effect pulling water out of it, although I imagine that would be MUCH slower than what happens while cruising.

And you still could have other problems that make it easier to drain than it should be. In any event, the RIGHT answer, even if there are other problems, is close that valve, then fix the other problems if you can find them.

 

[alnav]

ALEX
maybe you can solve the problem now:smt038:thumbsup:
because my vent filter was clogged, the techncian that came my boat to check this problem said to me CHANGE THİS VENT IT WAS HEAVY AND FULL , and he explained something like yours that can be the reason for leaking holding tank ,until there i agree with your comment but ;i use my head very very rarely, so i think its not belong to use head because we dont use usually choice marinas toilet only while long cruising we use (dont forget i bought this boat 31,12,2012)


YES , when the yellow level close it save the water in the tank

Sounds like your vent filter was either clogged when you got it or you may have clogged when you filled the tank. Doesn't really matter what kind of liquid got into the filter, either from the head or the fresh water you have been using. You will want to change that filter in any event; you will get smell in the boat or worse, if you ever do try to pumpout you might implode the holding tank if it's not vented.

 

[denizcan]

When you are cruising, water is flowing past the thru-hull fitting. Depending on the location of the thru-hull, this will produce either a high pressure (water trying to come in) or low pressure (water trying to go out) zone around the thru-hull. Think about driving the car with a window cracked open just a bit.

Due to the flow of water around the boat's bottom, I would suspect it is creating a low-pressure zone, which would tend to pull water out of your holding tank, even if the lines ran above the tank. Suction can pull water uphill, and it might even pull it through the macerator, depending on how that is constructed.

Also, if the tank is mounted higher than the water level outside the boat, once the hose is full you can still get a siphon effect pulling water out of it, although I imagine that would be MUCH slower than what happens while cruising.

And you still could have other problems that make it easier to drain than it should be. In any event, the RIGHT answer, even if there are other problems, is close that valve, then fix the other problems if you can find them.

the technician explain similar with your comment,my english is not enough to understan %100 of your reply but i understand that similar comments with technician
so to change the vent filter solve it , and last night(now morning in Turkey) i closed the valve so will not escape water from holding tank , and if i want to discharge i shoukd open because i know that if valve is closed you can not discharge your head (inside rules 12 miles from away)