Plan ahead.
 

I am happy to help with layouts, please call before you drill.

Hi golfnut,
I would like to here what your thoughts are on the OM4way with the 2" in &1.5" outs in particular the pump you would run throu it,
A little details of my tank 150gl 48"x 24"x 30" high , peninsular with 1.5" drain to OM supply pump (to be purchased) two returns in the back and 2 over the top to the front of tank and the OM drum is with the 1&3 2&4 ports
Thanks in advance

Ideally if you are looking at the tank and the overflow box is on the right, then you want to move the water clockwise, this will get surfactants being pushed towards the overflow box.
The supply feed for the pump can be buried in the rock-work in the center of the tank in your case and be split into multiple inlets to reduce velocity and the chance of pulling in critters etc, directing the pumps feed towards the overflow box will increase the clockwise velocity if you are going to drill then simply return the outlets from the 4 way back to the bottom of the tank just inside the rock work so they are not seen, point them parallel to the sand pointing away from the overflow to encourage the clockwise flow.
I wouldn't waste money on a 2" unit considering that this is a closed loop and there is no head loss, go with 1 1/2 inlets and 1" outlets and any pump with a 1 1/2 inlet/outlet,even a Dart doesn't require a 2" inlet in a C/L format, anything in the 3000 to 3600 range will give you more turnover than you need, likely in the 50x turnover rate in tank.

Paul