DE leaks into pool after filter turns off

Every time my filter turns off water from the filter flows back into the pool via the main drain. DE is entering the pool when this happens. I have replaced all the grids and also the multi port valve as I thought the DE was entering the pool during the filter running. But I noticed that the DE is entering the pool AFTER the filter shuts off. It only enters through the main drain. When I shut the main drain valve once filter is off no DE enters through the returns but as soon as I open the main drain I can hear the gurgling of water in the filter and can see the water flowing back through the basket towards the pool. And then the basket gets cloudy with DE and then I can see the DE enter the pool through the main drain. When I put the multi port on recirculate, waste or closed the water does not go back towards the pool. As soon as I put multi port valve on filter the water and DE goes back into the pool. I am at a loss to understand what is causing this- any thoughts?

Hi Jimmy;

It sounds like you've got an air relief (possibly, not by design) somewhere in your system that's allowing water from your filter to siphon back into the pool. That is NOT a filter defect; you'll need to stop the siphoning.

You've got two options: you can find the air relief (leak) OR you can install a check valve.

The valves below are inexpensive American made 1/2lb spring loaded, and should give you a reliable seal. (I've had so many problems in the last 2 years with American-branded Chinese-made plumbing components that I will NOT use them any more -- they've cost me WAY more than they saved me!) Amazon has a selection of valves from that company, so you may be able to find what you need if you want to use a different configuration.

A couple of installation notes:
1. Be CAREFUL to NOT get PVC clue into the check valve body. Lightly -- but completely -- coat the socket; slobber it on the pipe, but don't allow the pipe to drip into the valve!
2. Spring loaded checks should go on the PRESSURE side of the pump, at least 1 foot away, but between the pump and the filter.
3. If you want a check on the suction side of the pump, you need a swing check valve, but be careful to orient it, so that it will operate reliably.

King Brothers KC-2000-S 2-Inch Slip PVC Schedule 40 Spring Check Valve, White @ Amazon
King Brothers KC-1500-S 1-1/2-Inch Slip PVC Schedule 40 Spring Check Valve, Gray @ Amazon
http://ecx.images-amazon.com/images/...500_AA300_.jpg

Thanks Doc.