About six months ago my in ground spa stopped bubbling on its own. After reading online I used the trick of a vacuum to get it going. But, searching for a fix, I drained my spa and used the vacuum to clear my venturi pipe completely. After refilling the spa it worked fine, but after shutting it down and restarting it a few times water ended up back flushing out of the venturi pipe. Anyone have any idea what could be going on?