Thanks all of you for your quick replies.
Bodge, I live in a subdivision (...I don't like it but have no choice for the moment...), you know the type of place where all the houses are on top of each other... the back yard is a playground for all the kids!
Darringer, that's not a bad idea. I'll talk to the local car-wash and see if mud is acceptable for them (they probably recycle the water and too much mud could be a problem for their filters). I could do that as an alternative.
Powerjoe, Nikki, what model of gas pressure washer are you using (Pratt&Whitney or Honda engine)?
And what type of tank do you have to carry 35 gallons of water?
Thanks again for your help,
Yoken