Can you set one (or a pair) as high and the other low. Something like a drop of 1" turns the pump on until the high (the one you have rigged) turns it off?
Or are you saying it takes 10" for the high to sense.
You might be able to pump water in and use the high to open the bulkhead?
Greater Seattle Aquarium Society Member (GSAS.org)
General Auction April 18th 2009!!!
Community 60 gal T8 +CO2 +sump.
Clown Barbs 75 gal T8 +sump
Goodeidae project 20Long PC