We finally pulled the trigger and are installing our pool. It is going to be 18x36 inground vinyl liner, and completely DIY (well,mostly). While I am waiting for the excavator to show up I am trying to finalize my plumbing plan and I have a question. I am planning on 4 inlet lines (1 for main drains, 2 for skimmers, and 1 for a dedicated suction line) and 4 return lines (2 for wall returns, 2 step returns on one line, and deck jets on the last line). All will be 2" pipe. I see that most people use the 3-way valves and I cannot for the life of me understand why that is preferable to installing 2-way valves on each line. Seems to me this would offer maximum flexibility. Please enlighten me.