Hi all, I fitted a Fluidmaster 1/2" bottom entry fill valve in a toilet about 4 years ago, and it's all been problem-free until last week, when the seal against the cistern began to leak. Looking at again, I'm not entirely convinced about the sizes of the fittings: the water pipe fitting underneath the cistern is 1/2", the hole in the bottom cistern is 3/4". Looking at how the valve mounts to the base of the cistern, there's a rubber seal on the inside, but I'm not convinced that it's sitting well in the 3/4" hole. On the outside, there was only a wimpy plastic nut which barely covers the 3/4", hole with no seal that side. I've tried refitting it, and adding a 3/4" poly washer (from a previous siphon-repair adventure) on the outside, but it's still not sealing that well. So, some hopefully quick questions for you experts: Am I using an appropriate valve? Is it right that there's only one rubber seal on one side of the cistern mounting? Can you recommend anything to clean around inside of the cistern around the hole before refitting a seal? There's a small amount of limescale there which is hard to get to, and may well causing sealing issues. I'm resisting using citric acid or Viakal or equivalent to dissolve the limescale in case traces are left behind and attack the rubber seal. Thanks!