Originally Posted by MikeCC
Thanks - that's exactly the sort of thing I had in mind. Seems the one you have is the only size. Unfortunately the hole in the Avon is around 105mm diameter.
mmmm.... If you're very handy - there might be a way you could fabricate something very similar in that size... It's really BIG - almost the size of a CD - or even - domestic sewer pipe... If you go to a DIY/Hardware store - you can buy a bung for closing off a domestic sewer pipe. If you can neatly trim the shoulder off it - then you have the plastic disc part. Now you neet to get the two rubber flaps.... it's pretty easy to get hypalon or PVC from which to cut the thin flap - and I'm pretty sure it's possible to get a price of neoprene from somewhere who makes/sells/repairs wetsuits, etc...
Dunno - seemed like an idea - if you have the time & patience.... Might be something else there in the domestic waste area that I've missed!!!