Good Practice Guide

Waste connections to a dishwaster or washing machine

The nearer the appliance is to a sink the better, because the waste pipes are already in place. However it is still possible to install even if the nearest waste connection is some distance away.

The waste pipe should be 40mm or 1½'' in diameter. The flexible hose from the washing machine must discharge above the level of the top of the drum, otherwise the machine could empty by siphonic action.

If your dishwasher or washing machine is close to a sink, the sink trap can simply be changed for one which includes a connection nozzle. The machine hose is fixed to the nozzle and secured with a jubilee clip. If you do not wish to change the trap, a washing machine tee can be used to connect the hose to the existing sink waste. In either case, the hose from the machine should either be fitted with a non-return valve or be fixed (using a hook or strap) so that it is above the sink waste level to prevent water from the sink discharging into the machine.

If the dishwasher or washing machine is not close enough to the sink to connect to the sink waste, a separate washing machine standpipe is available, code. This can connect to an existing waste system, soil stack or be taken out through the wall to connect to drain. The hose from the appliance is pushed down the standpipe a minimum of 150mm (6'') and a gap must be left between the end of the hose and the water in the trap at the base.