Nor-cal,
On the older boats with shallow bilges and low free-board, we have experienced priming issues when using aerator style pumps. I would consider using a reversible. Also, with the height of the rear sac, you will experience passive draining through the fill line, unless a check-valve is used. This is not a problem with a reversible as the impeller acts as its own check-valve.
Check-valves are less expensive then anti-siphon. With an in-line check-valve, no need to have the line or anti-siphon above the sac, This may be easy with the bow pair, but going to be tough with the aft sac.
On boats with high free-board, looping the hose above the height if the filled sac does work. Dont know if you can accomplish this in your application.
I would stay away from the spring loaded check-valves commonly found at the hardware stores. They are problematic and restrict flow. Yes, as water pressure builds, the pressure will bleed off through the aerator drain pump.
Also keep in mind that aerator pumps are very suseptable to head pressure. The larger the hose, longer the run and higher the elevation, the more the flow slows. In some cases, the flow at the sac may not be any faster then that of the slower reversible pumps. They are a positive-displacement type pump and less effected by head-pressure.
Michael
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