What size grating are you using? I use 1/2" hardware cloth on the bottom of my brooder and the grow-out coop. The poop falls through or gets sratched through until they are maybe 14 weeks old, then it starts to build up. I don't know what size grating will be needed so older chickens' poop will fall through. I seriously doubt 1" opening would be enough but I truly don't know.
I would not count on washing it off. You really don't want it ti get wet. You can get smell problems big time. If you clean it out and really air it out, that's OK, but don't leave wet poop in there.
I would not count on washing it off. You really don't want it ti get wet. You can get smell problems big time. If you clean it out and really air it out, that's OK, but don't leave wet poop in there.