I was thinking the same thing, quite a bump!
I scrape all of the ash out, sometimes I sprinkle it in the bottom of the cooking chamber (Bandera) first and let it soak up the grease. I scrape that out quite well. The racks get left as is until next time I cook - it's then that I put them on the gasser, along with an upside-down water pan (wiped out), and turn the burners up high. This is about the only work my old gasser gets any more! When all of the smoke is gone, wire brush the grates. I think the grease, etc. protects them... after the wire brushing, my grates still look new, even though they are more than seven years old. I do occasionally scrape down the walls of the cook chamber, because I find some dry stuff that hangs on there occasionally (maybe creosote? yuck! So THAT's why we wait for the thin blue smoke :-) ) Never any water here...hell, I hate if if it even drizzles on it.
President, Canton, OH chapter, Weber Rescue Society.
-Leinenkugel's - keep drinking until you can spell it-