Help……..I a,m having troubles with my pool filter. we have a clear way filter. our pool is 24 ft round. the pool is 3 years old. we have a main drain. the filter seems to work fine when both drains are open. however when i close the bottom valve, it seems like it loses prime and never primes completely, then the return is sputtering. i cant hook up our ez vac kreepy khauler theres not enough pressure. i have backwashed the water is clear, so chemicals are fine, ugh i need help, PLEASE