I have a 15 year old 18x36, 36000gl pool. Last year I noticed one of 4 returns was not putting out any water. This year I have 2 of the 4 not working. They are off the same line as they are right arcross from each other. The pressure seems to be high also, its at 25psi and will slowly creep up to 30 in no time. The other other two returns are fine, they seem to have good pressure. I do have an air compressor, can I use that to blow it out? Im thinking if I was to put back all the plugs, like when you close the pool, and run the pump would that unclog those two lines? Thanks for any advice you can give me.