I recently noticed DE has been coming out of my main drain when the pump shuts off. I searched and found some good threads here that it is probably an air leak somewhere in my system, allowing water/DE to drain out of the filter and back into the pool. What I can't figure out is where the leak is. I have a Hayward 4820 filter with a Variflow and solar water system sometimes on. Some tests and observations I did based on those threads:
1) With pump running, loosen the air valve on top of filter. Air hisses out for a few seconds, and then water.
2) Shut pump down, and I hear a gurgling noise from the filter, and start to see cloudiness in the pump lid window. There also seems to be water coming down from my solar system (which has not been turned on for a week).
3) Pour water over connections when pump running, don't see anything funny.
4) Note my check valves, I have one on the outlet side of the filter between the filter and a Jandy valve that bypasses the solar, and another on the solar return. Both are pretty old no-name brand ones that could be the culprit.
5) For the 3 years we have owned this house, when the pump starts up we always get about 10 seconds of bubbles out the returns, a serious purging of air. I have never done anything about it, because the pool has run smooth using the TFP methods.
Thanks for any advice you can give on what to troubleshoot.