Soil pipe connection

[Phil the H]

I'm currently building an en-suite to a first floor bedroom and planning to run a vertical 110mm soil pipe to connect to an old clay pipe gully/drain below.
I've exposed the gully which was encased in concrete and succesfully removed the concrete and remains of old pipe from within the pipe collar. What Ive now found is that although it may not be obvious from the photo, the clay pipe is 3inch and looking at a recent CCTV survey of this drain what you can see is the up-stream end of an approx 2 metre section of 3inch before increasing to 4inch where it continues to a main access chamber.
My Qs are:
1 - Can I connect my new 110mm plastic into this old 3inch without later having to suffer blockages plus is that permissible under building regs?
2 - Because it will be difficult to cut the 3inch pipe behind the collar and simply clamp a rubber connector around the pipe (from the photo you'll see the pipe is beneath a raised patio and tricky to gain access with a disc cutter any further than the collar) how can I connect PVC to or into the collar and get a decent seal?
3 - If its a NO to the 4 to 3 inch scenario then I guess the only solution is to dig up the patio to remove the sections of 3inch, although hopefully you'll appreciate the amount of extra work involed in excavating an extra metre just to get down to the pipe?



Thanks in advance.

 

[denso13]

This should have building regs approval. Better to talk it through with the inspector as they will be signing it off anyway.

Should really be connected to the 4" though.

 

[Hugh Jaleak]

I'd be very surprised if BC will allow a connection to the 3" pipework, and possibly even more surprised if you did make such a connection and didn't have problems. In fact your first issue may well be making a connection to the 3" anyway, there is nothing on the market I know of that would allow you to make a connection to the 3" collar you have there, cutting that off to fit a Flexseal, (if they've indeed got anything suitable), would provide a perfect place for rubbish to catch and block the pipe...

I think you would be far better biting the bullet now, doing it all (properly) in 4", and then sitting back and enjoying the fruit of your labours, without being paranoid everytime a female uses the ensuite and what may get flushed....

 

[Ian H]

I’d rip out the 3” too. The structure it’s running under looks to be pulling away from the house.

You can get 83mm soil pipe, that would be the equivalent of 3”, seemed quite popular in areas near Burnley/Darwen for some reason.

 

[Phil the H]

Thanks for replies, I'd already been mentally preparing myself to excavate and replace the 3inch so I could sleep at night afterwards!
Yes, the raised patio was an add-on from the previous house owner although the gap hasn't increased for several years so I'm thinking its finished settling.