Hi,
After I vaccuum the pool, backwash and turn the pump back on for regular circulation, dirt I just vaccuumed shoots back into the pool from the returns.

When I backwash, I make sure to do it long enough to both run clear and to give it an extra 30 seconds for 'good measure'. The result is the same regardless how long I backwash for - once I turn the filter back on it shoots out dirt for about 15 seconds. It's a sand filter.

Thanks!