Ancient Soil Pipe Connection Issue

[denmancentral]

I had someone move my toilet soil pipe which involved changing the connection to the vertical cast iron soil stack. I didn't like the look of it and pulled it apart. I found that he had emptied a full tube of silicon which had solidified and was blocking about 90% of the pipe. I removed most of it. So far so bad.




The vertical stack is shared with flats above and below. There is a boss in the vertical stack which has an inlet for my flat. The photos show the (very old) rubber/plastic connector that was installed to interface between a modern plastic soil pipe and the boss inlet. It looks a bit like like an old WC connector and has a fairly small inside diameter plastic pipe as the second photo shows. It says' MULTIKWIK' on top. The whole thing was originally wrapped in a kind of bandage and covered in gummy resin.

I haven't tried to remove the multikwik interface, but i suspect that the metal boss is not a standard size. There may also be a kind of lead connector in between, which is what the next door connection uses. As it is, a plastic pipe fits pretty loosely inside but could be siliconed beneath the rubbery part. But the plastic pipe stops where the interface narrows, so I'm worried that water will run back under the plastic pipe end and will sit in the joint.

Anyone have any ideas for doing this properly? Note that I can't drill into the stack due to access restrictions so i have to use this inlet. Should I pull out the multikwik?

[lets have a look]

It could be a 3" soil not a 4" soil,you can get a 3" pan connector which is made of a stronger plastic not like the more flexible multikwik,you are connecting new to very old so it is trial and error