Thanks all!
Lowes here in LB is stocking a portable (hand-carry) 1700 psi Craftsman-labeled unit @ $99. I brought and tried it yesterday using the one nozzle that came with. Actually, an impressive little unit but I’d not wish one lower than 1700 psi. Should have gotten a unit when I brought the inflatable rib. Could have saved myself a lot of work hand-cleaning the bottom.
There is no paint on the bottom of the rib. I have no stern davits, no floating platform in the slip to haul out on, and no storage on a dock-side rack. I hoist it along side using a 6x purchase block-and-fall suspended from the spin halyard for interim “storage” out of the water, but I can’t do that easily with the OB mounted. If using, say, for regular harbor excursions near happy hours, I leave it in the water under the port quarter with OB mounted for two or three weeks at a time. Then remove the OB, haul it (dink) up and usually onto the foredeck and then invert it to clean the bottom, etc. With the pressure washer, I can now clean the bottom satisfactorily while the dink is suspended; i.e., no need to haul onto deck or dock to invert.
Yes. It’s all ridiculously cumbersome and inefficient. But adapting the spirit of Churchill’s remark about the democracy being the worst form of Government
except for all those other forms that have been tried...well, the same here on how to manage regular use of (in harbor) a 9.5 ft inflatable rib from a slipped sailboat.

Just FYI, putting on an anti-fouling bottom at the yard cost as much as the dink itself, if not more.