Does my dishwasher waste require a trap/ubend

[bryn]

In my boredom I thought I would renew the 40 mm dish washer waste piping. It basically goes from inside the kitchen through the outside wall and discharges into the gate/gully under the kitchen sink using 40mm pipe and elbows but no u bend/trap.
Its clearly not connected directly to the sewer and so my question is do I need to fit a bend/trap which I assume is to prevent sewer gases leaking into the house but the gully/grate u bend does that.
Much appreciated
bryn

 

[rpm]

The water in a U bend will stop sewer smells, wind and rodents, do you need one or not is your choice.