NOTE THAT IN THE UK (AS OPPOSED TO EUROPE) THE TAPERED END OF VITREOUS PIPE POINTS DOWN TOWARDS THE FLOOR. THE INFO ABOVE SHOWS EUROPEAN SPEC.
As with all vitreous pipe the bottom end narrows to a lesser diameter to enable insertion into other pieces of pipe (male is always on top). Key reason is that any condensation that trickles down inside pipe cannot escape. Straight lengths can be cut using a grinder and 115mm cutting disc (available from this online store).