Does your dishwasher have a reserve dispenser or just the cup & covered cup setup?
If you have the latter you'll need to wipe down the inside walls with hot water and a rag to remove as much of the residual soap. Take the racks outside and spray them down with a hose. Once you get the insides clean you should not have to much left in the pump & piping. Start it up and once the pan is full let it run a bit. Then with a wet-vac suck out the water. You'll likely need to do this a few times as you don't want it to froth up the suds by running it too long.
If on the other hand you have one with a reserve dispenser you'll need to open it up to get to the bottle and give it a good cleaning. Follow the same steps once you have no new soap getting into the washer.
I guess your teen has a weekend project ;-}