The engine seems to be pretty waterproof. I've cleaned mine dozens of times without a problem and never covered anything up. I wet the engine, hose it down with Foamy Engine Brite, let it sit a while, and then hose it off again. If there are really grimy deposits somewhere, I clean those off with a brush and some gasoline. I used to use Citrus Engine Brite, but I can't seem to find the stuff anymore.
Water can enter the ABS unit - the harness connection appears to be poorly "water proofed".
A little RTV gasket in a tube, a cable tie around some oven duty plastic(Reynolds Oven Bags) should help..
I used to think that the pressure washer was the greatest thing to hit the market place. They are great for cleaning concrete...
Now , I'd love to have a little steam cleaner, but I know of nothing on the market with any "gut"..
Hot water will have to suffice for now.