[Myka]

Since you have two return lines, I'd use 1.5" from the pump to a tee where it splits to each return. I'd try to get that tee as close to the bulkheads as is feasible. Run the 1.5" right into a 1.5" tee, then slip a 1.5" by 1" reducer bushing into each output, and run 1" from there to your bulkheads. Depending on how it ends up getting plumbed, I often like to put a ball valve on whichever return line is shorter/straighter so I can throttle it back so it gets even flow with the other one (if that matters to you).