Question: I fitted a new tap and waste outlet to a small basin, because the new outlet is shorter than the old, the plastic pipework no longer reaches (see photo) I can force the parts to mate but I don't like having the pipe under a lot of strain and it doesn't seal properly (I havent tried applying copious amounts of plumbers putty).

![pipework](https://i.stack.imgur.com/6L94M.jpg)

I am considering cutting off the white-painted down-pipe (at right of photo) and using a solvent-weld straight coupling to insert a new section of pipe to raise the pipework about 1 cm.

The existing pipe has an outside diameter of 36 mm.  

The pipes available in catalogues are listed as 32 mm or 40 mm.

I understand that a nominal 32 mm plastic waste pipe has an outside diameter of 34.5 mm. Is this the right pipe?

Answer: 
![enter image description here](https://i.stack.imgur.com/ItRqy.jpg)

Cut where marked, but adjust the location so you've got clearance to work later.

Seeing as you only need a couple of millimeters, you might be able to get away with buying only the coupling connector similar to this:

![enter image description here](https://i.stack.imgur.com/DD7Bd.jpg)

So a good straight cut where marked, insert the connect and solvent weld it back into place. 

Take the cut piece in with you, and just make sure you've got a snug dry fit in the store.
No need to actually figure out the exact diameter. Just buy the piece that fits.
So far I have discovered there are at least two incompatible types of "32mm" plastic waste pipe.

* "**solvent weld**" PVC or ABS pipe with an inside diameter of **32mm** and outside diameter of **~37mm**.
* "**push fit**" plastic pipe with an inside diameter of **~29mm** and an outside diameter of **~35mm**

Because of the difference in diameters, you can't use push-fit fittings on "solvent weld" pipe and you can't use solvent-weld fittings on push-fit pipe. I guess this is deliberate to stop people trying to use solvent to weld a pipe made of a material that the solvent won't melt.

Diameters above are approximate measurements made with a cheap vernier gauge.