Just as an FYI - I just backwashed my filter and left the pump off, but w/ the multi-port set to "filter". My backwash hose fills up to the return pipe level. I never did get around to blowing into it, but now I think I don't have to. Seems like a bad multi-port to me. Guess I'll be replacing that sometime.... Right now it's not causing me enough grief to spend the time & effort.

-Rob