Cannot get my overflowbox to fill and hold the siphon

[mark]

read to add a small PH such as a MaxiJet and attached the venturi line to the top of the U-tube and just leave it running all the time. Pulls out any air and helps maintain the siphon

[karazy]

im guessing this is an e-shopps overflow, and what im doing with mine is drilling a hole a little bit behind the peek of the U-tube and siliconing in some airline tubing connected to a aqua lifter pump