1.5" 43 mm solvent waste fittings, commonly called 40 mm solvent.

Outside of the pipe and inside of the fitting should be around 43 mm.

Designed to be used with solvent cement for a watertight seal.

Available in many different styles of fittings, please see picture and selection list
New 1.5" BSPF thread Pump connector 43 mm socket with 56 mm spigot outer
suitable to fit any 56 mm fitting or 2" rubber