Many years ago when I first started working at the college, I was assigned the task of pressure washing the brick on the outside of the buildings on main campus. I used a 2,500psi pressure washer which was powered by a 11hp gasoline Briggs and Stratton engine. While filling the gas tank on the unit, a faculty member was walking by and proclaimed:

"So that is how you are getting the outside of the buldings so clean; you are using gas!"