I looked at some of these issues and decided the following:
Each bilge pump gets its own thruhull.
Each pump gets its own hose with a clean a shot to the thruhull as practiable.
Only one has an anti-syphon which I left in place as it has not caused any trouble, one has a high loop to prevent water from entering unless boat is well underwater, in which case pump is likely running.
Bilge area is large enough to not have pumps restart after pumping water so don't know about that for your boat.
If you are going to share hoses and thruhulls, I would use a Y valve and a simple on/off for the large pump. Idea being that the large one is just for another incident in which much manual pumping is needed. Look at your boat maybe this does not need a thruhull at all. Maybe you have a way of just leaving the hose coiled and ready to be fed though something to get it over board? Something to consider if another thruhull is not an option and you want that back up.
Better or same diff to leave the small one on when you are not at the boat. Not that it will use much less power, the amount of water leakage determines that but it will operate a little longer when your battery is dying. Big pumps draw big current.
Edit: You might want to consider keeping only one battery on the boat and replace it with the other one (fully charged of course) when you do your regular inspections. This will also get you to check voltages regularly and give you an idea how long you can ignore, I mean, extend the periods between inspections. When you go away for a long time leave both fully charged in the boat. AGMs are great for this work as they do not selfdischarge much and are easier to carry around.
Have faith that the oceans are going to rise and flood the world, that plague and pestilence brought on by Climate Change is going to punish us for not believing. Please do as they say it is our only hope. :P
Last edited by Architeuthis; 04-13-2010 at 05:17 PM.