You may want to give wake Makers a call on the siphon problem. The guys there focus primarily on ballast systems and may have a couple suggestions for you. While cruising their site a couple days ago I ran across this anti-siphon valve (http://www.wakemakers.com/1-inch-vented-loop.html
). Seems like this may do the trick for you. Don't know if this will solve your problems but it may be a start in the right direction.