I’m not so much asking how to clean it, but how much water you all think it would take. I just have my 50 gallon tank, probably don’t have access to a water source although the school may have an outside spigot somewhere. The building is too far away for me to run a supply line.
I’d say 50 gallons is more than enough water for that. I had a detached 2 car garage with vinyl siding & no water supply on site a while back. I filled a 5 gallon bucket with about 2% & applied it with the Ryobi 18v then rinsed with a 30 gallon buffer tank.