Adjust my bilge pump hose/ propane locker hose routing?

[redpointist]

One propane locker drain goes currently goes out its own thruhull, but the other propane locker currently shares its thruhull with the bilge hose, with them being teed together before the thruhull. If we were actually storing any propane I would think this would be very bad and allow fumes in the bilge, but since we dont have any propane on board I havent considered it an urgent problem.

Im replacing the bilge hose, and before I cut I I need to make a decision. Im thinking itd be better to tie the two "propane lockers" together on one thruhull, and let the bilge hose have a thruhull by itself, to reduce the amount of hose/ drain back which is leading to a bit of pump cycling.

I wonder though, if the "propane locker" tie in was done to act like a siphon loop for the bilge hose, and if I were to adjust the routing if I would need to add another siphon loop, which might defeat the purpose of changing anything?

[mike d.]

The fumes could only get into the bilge if the bilge pump had no head! IE If the water it sucked out of the bilge drained out of the hose, and both the discharge after, and before the hose, not to mention, the water in the pump drained, and the valves in the pump open both sides to the air! Even with an impeller pump, (non piston/valve) pump there should be water to stop air migration back to the bilge. Not the b est set up, but !