So first the background.... 40 by 20 in ground with 3 return lines and 2 skimmers. 2 of our 3 return lines will not push water. I have capped off 2 lines and tried to run water through just one of the deficient returns but nothing will come out. However I can push water through from the pool side with a hose on one end and a shop vac sucking from the other where the return pipe comes out of the ground to go to the filter. Also a pool service tech was able to push air through from the filter side to the pool side with a 5 hp blower. Any thoughts?