Cannister Filter Problem

[grendel88]

I am setting up my first saltwater tank and have now hit an unexpected snag. I have 75 gallon aquarium with a 20 gallon sump. Inside the sump is some base rock and a protein skimmer (Coralife). I initially intended to use the cannister to suck water out of the sump and deliver it back to the main aquarium. When I put my my plan into action, I found the cannister will not suck in water. Not only that, when I turned the cannister off to check what the problem was, the water siphoned back into the cannister and it started overflowing, even though I had it shut. The cannister is used so I dont have the diffuser or intake piece. Do I need to restrict flow? ( I only have two 1 inch hoses attached to it) Are cannisters only made to suck from a tank that sits higher than them?

[phrog]

I ran a canister on my 30g for about a year. The canister did not suck water but siphoned it by gravity and used the pump to return it to the tank.