Hi. The pipe that drains water and DE from my filter during backwashing is clogged (the drain line goes directly to the sewer). I applied pressure to the line via garden hose and a pool maintenance man applied pressurized air. In both cases the clog held (the pool guy said he's never heard of a backwash line clogging). I'd like to know if anyone has heard of or experienced this problem and, if so, what the solution was. Thanks in advance for your advice.