Ok, my pressure washer uses a garden hose on the input, and 20 feet or so of high pressure hose with a wand and nozzle on the output.Touché! I guess a hose is still needed...No nozzle at the hose end, though...
I don't get why so many people want to use high-pressure sprays on their RV or car. The infatuation that Americans seem to have for power anything? There is no reason to power-scrub - a soft wash brush, mild carwash detergent, and a gentle rinsing spray is all that is needed. Maybe a foam gun if you prefer.
If you use a pressure washer on the roof be very careful. Even on the sides there are places where caulking is used and excessive pressure can make leaks from loose caulking.I love these on my pressure washer
The amount of water to be added should depend on the size of your waste tanks. If your RV has a 20 gallon tank that is 1/4 full and too much. I suggest that you think in terms of about 10% the amount your waste tank holds and then only if the RV will be used again soon. If in storage for the season the tanks should be flushed out and left empty.After dumping the black tank you should add around 5 gallons of water to the tank to help break down any solids left behind after dumping. Going down the road will really help out also.