Zanussi ZWD 14791 W User Manual page 30

"U" piece
supplied
When discharging into a standpipe ensure that the top of
the standpipe is no more than 90 cm (35.4'') and no less
than 60 cm (23.6'') above floor level.
30
Place the drain hose into your standpipe, which should
have an internal diameter of approximately 38 mm thus
ensuring there is an air break between the drain hose and
standpipe.
38 mm (½")
standpipe
diameter