CH, yes, it could be only the gasket (which would save you $). As for the water in the backyard, I don't know the plumbing so can't say for sure. That's why I suggested the bucket test to see if the pool is still losing water. Unfortunately leaks sometimes appear in sets, you fix one thing but the pool is still leaking - it's frustrating but you've got to tackle or eliminate one thing at a time, but I can almost guarantee you that the gasket in your multiport is shot. Sometimes leak detection can take weeks to find , but 'slow and steady wins the race'. I'll keep my eye on this and help as I can!