I just installed a brand new Dishwasher. Only used once to run a cycle. Now it smells like sewage. Awful:yak5:. Anyone ever have this happen? Its killing me.

Check the drain hose, make sure its routed properly. Should be before the "elbow" to prevent the stench/methane gas from coming back up.

The drain hose is above the P trap.

I suppose that would have been too easy.

Make sure that the new drain hose goes to the highest point under your sink, When I install a dishwasher I try to wire tie it to a sink clip
This is to create a air gap in the line. a portion of the hose needs to be higher than both the inlet and out let of the hose.

Make sure the outlet of the hose goes into the sink drain side of the trap