I have a 18x36 inground salt water pool. It worked fine after having it vacuumed but suddenly stopped holding prime in skimmer basket. When I turn filter on to both skimmer and main drain line, I lose prime. It will hold prime on just main drain. I have tried clearing line with drain king and switching handle between settings with no luck! I feel like I am at the point of having a plumber come out to blow the line. Any ideas would be appreciated!