When we started our filter this year, couldn't get the sight glass to not leak. Doesn't leak when in normal filter mode, but when I switch to backwash it leaks for several seconds then stops leaking and when I switch to rinse or waste it leaks continuously. I hand tightened as well as I could and even had someone else try to tighten it down - neither of us could get it to budge any further and leak was still there.
Also, when in filter mode, I get a slight accumulation of water in the backwash hose. Not a huge amount, but figure it's indicative of an issue somewhere also.
Neither of these is a huge deal as this filter is out the door soon (laterals are busted too apparently) - but I figure if I understand why these things are happening I'll better understand the mechanics of the filter in general.