My 20x40 vinyl IG has 2" piping all around (found poolforum before my build, thank goodness). My PB was reluctant to use 2", but I convinced him. I have 3 suction lines (main drain and 2 skimmers) and 2 returns. The suction lines are 2" with 2" fittings (at least the skimmers are - don't really care too much about the main drain) all separate lines to the pump.

The 2 returns are 2" separate lines after the SWG, BUT, they have 1.5" fittings at the pool! I just checked yesterday. The fittings are clearly glued inside the 2" pipe and take regular 1.5" caps. Never really occured to me to even think about it until I replaced my 2HP SuperPump with an Ikeric variable speed pump and got to thinking/calculating flow rates, etc.

I have tried pretty hard to minimize restrictions in my piping, especially since I am using solar. Anyone think that these smaller fittings are going to be a problem in the long run and are worth fixing (probably have to lower the water, rout out the old fittings, possibly enlarge the opening in the pool wall, yikes)?

Another thought I had was to convert my main drain to a "main return" (or possibly 3-way it so I can have it whichever way I want). This actually might be useful with the solar in the early & late season when pumping in the warm water at the bottom of the pool is *supposed* to be more efficient. And it actually wouldn't be difficult due to the way my piping runs. However, not sure if it is worth it since I imagine that there would be very little flow to the main drain "return" since it is about 7 feet deeper than the other returns.

This is sort of a water-cooler issue at this point, but I would love to hear opinions!