We have an inground pool with a sand filter. Water goes to 2 returns, the Pool cleaner line, and a waterefall line. I've read a lot of the posts here but can't see anything that addresses how to blow out these lines when they are "behind" the sand filter. Do you insert the compressor or shop vac into the air release on the filter? My pump & filter do not disconnect. Any help anyone can give would be greatly appreciated.