plumbing problem overflow hose

Ohio BigDog

I have a all-glass with megaflow overflows the drain line calls for a 1 1/4 ID hose so i got the flexspa 1 1/4 id hose problem it slides right on i put two clamps on it still leaks .I also tried getting the 1 1/4 pvc to screw on the threaded part of bulkhead but it wont screw very far on. i can get it on about three threads . any one have this problem if so what did u do to fix? thanks Jim