If you were redoing it (as you are), seems that the most common setup now is to have taps for washing machine underneath the trough and the waste is also handled under the trough in an arrangement similar to how a dishwasher is done, i.e. a sort of angled 3 way connector on the S trap for the trough.
at least, thats how ours was done - no tape on the wall (above the trough or above/behind washing machine), no 'hole' to put the waste/drain into in the trough.
then again, the trough we got is an undermount one anyway without that 'waste' outlet.