Did what you said and think t's the flush pipe. Apparently it's supposed to be pushed 2 inches inside the syphon. Having trouble now screwing the cap on at bottom of syphon. The rubber washer seems to be stopping me. It didn't before. Should it be flat side up?Yes, what I meant was, If the flush pipe is pulling it slightly, then it’ll leak. Try removing the flush pipe first, leaving the syphon in place with a small amount of water in the cistern and see if it still leaks - if it does, you know it’s bugger all to do with the flush pipe.