Is there a preferred fitting for the initial fittings on this pump? I know some web sites recommend the pentair union, buy I was wondering what else can be used. The rest of my piping is 1 1/2". If I use a 2" nipple into/out of the pump instead of the union I can put a 2" coupling on the nipple and put the 1 1/2" bushing into that and continue. Is this ok or is there a better way?