Joining into existing WC waste pipe

Roger44

Hello
We're fitting a new toilet and want to insert the new grey waste pipe into the existing black pipe? What is the best way of doing it?



Thanks in advance

Ron The Plumber

Gray, that not for waste, you want white PVC, gray is electrical.

Connection done with fernco rubber couplings.

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Roger44

Thanks Ron
I'm in France where grey is used. I googled on Fernco and found many other instances of DIYers facing the same problem as I am. I have learnt :
-Fernco and similar couplings may or may not be unauthorised under the house (but nobody will check what I'm doing)
-another solution is a slip coupling, I suppose the 'Y' has 2 male extremities, but you have to be nifty and fast with the glue and of course you can't put any glue on the inside of the slip coupling.

I'll tell you more. The black pipe is some sort of fibrous material I haven't met before, I was able to make a hole in it by twisting a screwdriver into it. The surface is slightly mottled. Cement and usual PVC glue hold fast to it but bathroom silicon paste not so well.

The new toilet is about a yard away from an external 20" stone wall and the concrete floor has to be cut away in this zone for other reasons so it would be easy to lay a complete new PVC pipe passing under the wall alongside the black one.

Just under the ouside edge of the wall the black pipe is immediately joined to a smaller diameter 90° elbow PVC pipe which immediately disappears down, airtightly cemented, into a 1.5" thick soft cement lid which is artightly cemented onto some sort of very large concrete structure. I could open a new hole in this concrete lid and airtightly cement in my new pipe. I'm an experienced DIYer.

Ron or others, what would you do if you were in my boots?

Roger44

Thinking about it, I'll take more photos and post them tonight. There's no rush, I'm just retired, it's an old farmhouse my (courageous) son has bought so there's loads of other work to be getting on with.
Roger

Roger44

Hello
You can see in the first photo I cut a channel today into the floor up to the wall and a bit under. Dead easy. I learnt also that the concrete airtight box outside belongs to the house, so I can cut a hole into its lid. I rather think the simplest is to lay a new pipe for the new toilet and leave the black one alone.


Would you choose this solution if you were me. Would there be any air vent problems?
Roger