Kitchen sink back filling

[billy_smith]

I've got a problem with a kitchen sink, when the washing machine empties it fills up the sink bowl, the sink is not choked as when the sink is filled and emptied it runs away perfectly.

The trap is one of the McAlpine W/M WM11 traps.

I fitted the kitchen sink with plumber I work with but I'm getting sent back to the job myself tomorrow and not sure where too look next (the plumber I work with is off and said I should manage fine !!)

Anyone any pointers

 

[PrenticeBoyofDerry]

The things to look at are the size of the waste pipe, normally 40mm deals with both W/M and kitchen sink.
Then the route in which the waste flows between the two and how they are connected and if there is anything else connected to that waste pipe causing blockage/backfill issues.