ok, i'll explain it as best i can, thomas...ermmm danny
3 pieces of pipe, 1 T piece, 1 pump
pump goes in tank with pipe no. 1 coming up to the top of the tank and into the T piece
T piece has pipes 2 and 3 which are different lengths running into sump but ends not submerged, pipe 2 runs straight down to sump, pipe 3 goes a bit bendy to create a U bend type effort
when pump is running, flow goes into both but as pipe 2 is direct water flows freely through
pipe 3 fills the U and stops
when the pump stops, air is sucked up the U (pipe 3) by the weight of water in pipe 2 and the syphon is broken
da der.............