New pool guy backwashed pool today and during process fairly good amount of DE and sediment flowed out of returns. He indicated he checked bag in separation tank and washed off well but admits that he has no other pools with separation tank and is not familiar with them. Our first pool had DE filter which we loved but backwashed into waste line. We never had problem with DE returning to pool. Could it be he didn't properly seat the bag back in tank or is some loss normal with these tank systems?