Sink Drainage Solved
After creating a vent stack into a grey water bucket, leveling, re-leveling, checking level, checking with dealer (not helpful) on the slow drain issue. I finally solved it.
The drain on our trailer 1970ES for the sink sometimes drains marginally, sometimes not at all.
After the dealer saying it "drains normally" and not knowing what normal is, I did some poking around. If you remove the drawer below the sink you can see the flex hose (dishwasher hose) they use for the drain.
The problem is that when in the up position, it creates a p-trap and normally there isn't enough water pressure or vacuum created to pull new water through the trap. Unless connected directly to a sewer line, you do not need a p-trap which is meant to block the sewer gasses from coming back in, and you are only doing grey water anyways.
You can just lift up on the hose and it will drain a full sink in under a minutes. To avoid doing this during our trips, I tied a string about 6" from the outside wall to pull it up when in use so gravity will do its job correctly. Probably don't need the vent setup unless the sink is full either.
The vent setup is simply just a PVC threaded connection for the drain, a short piece connected to a Tee and 2 longer pieces , one into our grey water jug and another high enough to clear the top of the sink, just loos fit it works fine and stores under the bed.