We have a Lewis and Clark portable camp kitchen that we connect to the outside shower and use the hot water for dishes. It is very heavy and folds up like a suitcase. Photo below:

I've been also looking at these plastic fish cleaning stations. Mendards home centers just had a sale where these were only $39. The Amazon price of $80 seems too pricey.
Amazon link You can use it as both a table and a sink. I like the tall faucet. You could easily get a bracket so it could mount on the side of your RV where the exterior grill would mount.

As others have said, the drainwater goes in a 5 gallon bucket.