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Discuss Fitting advice for 2-in-1 Combination toilet/basin in the DIY Plumbing Forum area at PlumbersForums.net

Ric2013

Plumber
Messages
2,839
You really do need to cut in. It isn't really possible to make a 110mm strap boss as you can't really drill a 110mm hole into a 110mm pipe (think about it), hence they don't exist.

I do see your point, though. Your pan ID is likely to be around 80mm, so the restriction would indeed be only a few mm (were it a water supply pipe the restriction would be less of an issue and I have myself gone from 22 to 15 to 22 to get through an existing hole I did not want to enlarge due to the presence of asbestos). The problem is it would be a step in an upward direction with a waste pipe that is designed to be but partially filled, and you have solids in that pipe. So it would only be a matter of time before a bit of paper or a lump of faecal matter sticks on the step and then you inevitably have a regular blockage where it is least desireable.

Stick some photos up of your soil pipe and I'm sure we can advise you if you get stuck.
 

Ric2013

Plumber
Messages
2,839
If this is ground floor, there could be possible issues relating to how close your intended tee is to the underground bend where the stack becomes horizontal. There is a minimum recommendation of 450mm, but I have seen that rule broken without any obvious symptom. As I say, if you really want to DIY this, some photos and a sketch would help us help you.
 

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