My spa drains back into the pool overnight. I suspect this check valve, which appears to have been replaced before, is the problem. It's in a tight spot plumbing-wise, so I'm curious if it's possible to remove the PVC elbow from the jandy 3 way valve, and reconnect a new fitting into a new check valve? If I have to remove the jandy it becomes a larger project with a lot of knock on fitting replacement.