The search works..
So, I have no grey tank on my '72 safari 23'.. I just about figured as much..
The grey water collects all by itself in the outlet pipe...
A light goes on in my mind, expaining the clean water that came out of the little cap in the drain cover.. SO... I need to use the never used, but carried faithfully blue tank, all 30 gallons of it, that I have had for 4 years.
I think that adding a grey tank is way above my capabilities, so I have to adapt to the blue problem... In a full hook-up site there is no problem because it all goes down the same hole, from the same hole.
The black tank is above the floor, in the box under the stool... I see. Not much room in there at all, and the shower is indeed lower than the tank, so that is why it got really yuky. Isn't this an adventure.
Thank you guys, you have cheered me up considerably - now at least I know what is going on in there.