Here are the directions for my overflow.
To start water flow in the siphon tube remove the siphon tube from the prefilter. Insert a length of airline tubing into the siphon tube about halfway or to thhe midpoint of the bend. Kwwp this airline in place and put the siphon tube backk into position in the prefilter box so both ends are now under water. NOTE:: The siphone tube goes in the small chamber of the outer box, NOT inside the standpipe. Now suck on the airline tubing drawing out the air and filling the siphon tube with water. Immediately remove the airline from the siphon tube. The water will begin to siphon out of the inner box into the outer box and will stop as soon as the water level in both inner and outer boxes are the same. From lifereef products.
HTH
Jeremy
PS Let me know if this works
PPS: Normally you only need to post your question in one section.