Originally Posted by austinsdad
Just wonderin' why the outlet size of the pump wouldn't determine that.
The water from the return pump is under pressure, so the line don't need to be as big.
Return line is under gravity only, so it should be bigger to account for the lower pressure. As others had said 1" should be good for 600 gph
. Although if you are doing a Durso or a Stockman, 1.5" or 2" is better. The system is quieter with a bigger drain.
<There is no problem using a bigger than needed return drain ... you are controlling your water level at the overflow. A bigger drain simply means there is more air in the line. To reduce noise, you want your drain big enough that the water forms a sheet on the drain surface & goes down in laminar flow, without turbulance. The other method is to use a small enough drain that there is no air at all in the drain - ie the drain is maxed out in flow. This is quiet but risks flood, so you should have a 2nd (some even have a 3rd) drain set slightly higher as an emergency backup. >