I know this has been covered on here before, but I can't find an answer specific to this. I have an old, very old WC, which has a P-trap directly fitted into the spigot of a cast-iron waste. There's an exterior 4" cast-iron pipe, and an angled tee comes through the wall, with a flared spigot on the end. The WC pan fits directly into this socket, and appears to be'sealed' with hemp and plumber's mate compound. I want to (need to!) replace the toilet, and I'm intending to use one of the adapters with the ribbed rubber insert, to fit inside the spigot.
The question is, how do I know what size of adapter I will need, before taking the old toilet out. Is the adapter supposed to fit inside the flared end of the existing spigot, or am I supposed to cut that spigot off, and fit the adapter into the 4" pipe?
We only have one WC in the property, so I need to have everything prepared beforehand. Once the old pan comes out, it looks like it will fall to bits, so can't go back in again, even temporarily...