R6981 HORNBY ex-GWR Siphon H W1429 in BR crimson (freight livery)

Siphons were most commonly attached to the rear of passenger trains, due to the need to quickly transport the enclosed milk from farmer to the milk processing facility in the shortest possible timescale.

Often Siphons travelled singly, although on the most used routes from Devon and West Wales to Paddington railway station, express milk trains were scheduled.

After World War II, the milk companies began to use road transport to move milk direct from the farm to their dairy processing units.

This resulted in the earlier Siphons being fully withdrawn, and the later dual-bogie versions being used to transport parcels, after they had been fully sealed and their vents closed.

After the introduction of specialised parcels vehicles, the Siphons were often used by the engineers department, with ENPARTS in large letters on the side transporting spares around the system