Standard household bleach diluted, with a soft scrub brush on a pole. That takes care of heavy grime and mold/mildew.
For deeper cleaning
and to get rid of the chalking: Follow that up with Nautical Ease inflatable
boat cleaner - best stuff I ever used https://www.yachtingessentials.com/p...at-Cleaner%20/
Spray it on, spread it around and let it sit 5 mins (best in the shade so it doesn't evaporate as fast) hose it off. Repeat if needed. If you have chalking you will see it run off in the rinse water
Follow up with 303 UV protectant.
PS - wear protective gloves with all this stuff.