I just finished replacing all the holding tank hoses. It was a tough job. I used Shields Poly-X which is supposed to be lifetime guaranteed against permeation. It's very expensive but considering the many low / flat spots this system has I think it was worth it. I also inquired with IP about why this boat has no vented loop on the head intake and also the logic of the other vented loops, here are the responses from IP;
"The top of the head on the 370 is always above the DWL and open to the atmosphere, even at extreme angles of heel so the vented loop is not necessary on the intake and direct overboard discharge. The macerator has one because the holding tank is below the DWL and without a vented loop there would be the possibility (with failure of the valve in the pump) of a partially empty tank filling up with seawater. This would not be a disaster, but very inconvenient."
"The vented loop under the sink cabinet stays above the heeled waterline until about 30 degrees of heel in flat water. This is very close to the point where the head starts to be under the heeled waterline. Sometimes when designing a system aboard a yacht, there is not a defined point where you must install a certain piece of safety equipment such as a vented loop. Could you exceed 30 degrees of heel? Absolutely. Does it happen very often? No. Would it happen at the same time as the events that would lead to siphoning of water back into the head? Even less of a chance. In this case, the height of the head and the vented loop are very close at 30 degrees. Of course if this happens, there would most likely be a cyclical changing of the angle above and below 30 degrees, which would complicate the chances of a siphoning event. I would not recommend removing it."
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I just finished replacing all the holding tank hoses. It was a tough job. I used Shields Poly-X which is supposed to be lifetime guaranteed against permeation. It's very expensive but considering the many low / flat spots this system has I think it was worth it. I also inquired with IP about why this boat has no vented loop on the head intake and also the logic of the other vented loops, here are the responses from IP;
"The top of the head on the 370 is always above the DWL and open to the atmosphere, even at extreme angles of heel so the vented loop is not necessary on the intake and direct overboard discharge. The macerator has one because the holding tank is below the DWL and without a vented loop there would be the possibility (with failure of the valve in the pump) of a partially empty tank filling up with seawater. This would not be a disaster, but very inconvenient."
"The vented loop under the sink cabinet stays above the heeled waterline until about 30 degrees of heel in flat water. This is very close to the point where the head starts to be under the heeled waterline. Sometimes when designing a system aboard a yacht, there is not a defined point where you must install a certain piece of safety equipment such as a vented loop. Could you exceed 30 degrees of heel? Absolutely. Does it happen very often? No. Would it happen at the same time as the events that would lead to siphoning of water back into the head? Even less of a chance. In this case, the height of the head and the vented loop are very close at 30 degrees. Of course if this happens, there would most likely be a cyclical changing of the angle above and below 30 degrees, which would complicate the chances of a siphoning event. I would not recommend removing it."