Plumbing: waste pipe sizes

cliveb

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Hoping one of the resident plumbing experts can answer this.

In the context of plastic waste pipes (outlet from a bathroom basin), is the defined size the inside diameter of the pipe?
I have need to cut about 1cm out of the outlet pipe, and was intending to use a push-fit coupler to rejoin it (https://www.screwfix.com/p/floplast-push-fit-straight-coupler-white-32mm-x-32mm/11632).

The inside diameter of the pipe appears to be about 31mm; its outside diameter is just over 36mm. But I guess my readings could be out by a mm.
The only sizes of coupler I can find are defined as 32mm and 40mm.

And BTW, do these push-fit couplers actually do the job, without the need for any glueing or welding?
 

Bunkermagnet

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Hand basin you might do in 32mm. Bath and other plumbing (sink/appliances etc) you would do in 40mm
Different brands are slightly different in their diameters by fractions. Personally, if possible I would put a compression fitting on.
Anything with a rubber seal like that is push on, not glued on.
 

cliveb

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jim8flog

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Bearing in mind dependent on age it might be imperial ie 1.25" hence your reading being slightly out. Compression fitting still fits.
 

cliveb

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Bearing in mind dependent on age it might be imperial ie 1.25" hence your reading being slightly out. Compression fitting still fits.
Thanks. The bathroom would have been redone less than 7 years ago (when the house was refurbished by the previous owner), so my guess is that it's metric.
Far more likely that my measuring was a bit inaccurate!
 
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