I've recently had a leak from under the toilet cistern. I removed the Siphon to see if the washers needed replacing (which they appeared to do), however I noticed that the Siphon has. 1.5 inch outlet, and the cistern has a 2 inch hole. Who ever fitted it had filled this gap with silicon.
If its a low level cistern (flush pipe connects from cistern to pan) then you have a whole dfferent ball game
The cistern you have has a pull or lever handle doesn't it?
It will not have a push button type of flush, in that case the sealing mechanism from the cistern to the flush pipe will be via a compression type fitting, I have absolutely no idea how silicoon was holding in the water, you must have had some type of cobbled together washer nut arrangement
take a photo and post it here lets have a look at the rabbit
I put it all back together yesterday so we could use the toilet for a bit, haven't got a bucket to chuck water down with, so i can't get a photo of it in pieces.
However I can describe all the pieces. Between the siphon and the cistern is a rubber washer. Under the cistern on the flush pipe itself is a large nut followed by a hard plastic washer, followed by another rubber washer. The gap in between the whole lot is filled with silicon.
Below is a photo of the underside of the cistern showing the nut.
Sorry for the lack of photos.
I'm thinking maybe i should just get another siphon that's the correct size?