Originally Posted by krap101
ive heard you dont need to match the pump at all you just need an overflow box and when the water level goes under a certain point it stops siphoning until the water is pumped back into the tank. ill try and find the site
With too much pump, the sump empties too fast (faster than the overflow can fill it) and either the tank floods or the pump runs dry. (this is assuming no fancy cut off switches). Both are bad.
With too little pump the sump level will rise and the tank level will drop up to the level that the overflow box is set. Then the sipon/overflow decreases so that the sump stops filling. So it is best to use a smaller pump than your overflow, you can regulate tank volume and sump volume by the overflow hieght. An overflow that can flow faster than your pump is best for safety and convenience. So decide how much pump flow you want, then build or buy an overflow that is greater than that. How much greater? Don't know. I never measured the ones I had, bought them complete.
But it would be trouble to have a pumnp that is faster than your overflow.