Cat Litter SCOOP ....not cat litter. You probably know but just clarifying. They really don't care about the filth.
I really wouldn't worry about 'washing' it...you really want to keep it dry.
Lining pan with a single sheet of good vinyl might help,
less likely for poops to stick than the metal.
A dust pan might work to scoop out the poopy shavings.
Sand might work for you...but it could freeze solid in your winter.
Granular Sweet PDZ would be a bit less likely to freeze than a fine sand,
I use a mix and the wet ones freeze solid in the sand, can be hard to get up.
Either may well jam the slider track so might have to scoop with coop door open.