...once. Just show that even you aren't too good to do the hard stuff. Don't waste your time washing dishes when you actually need to be doing other things.
If he does it just once, I question his motives. This repeated behavior shows his true conviction.
His motive? to show that no one is too good to do the hard stuff. Its a stunt, but its a lesson too. Everybody will get that.
I know if I have a busy few days and the housework starts piling up my heart sinks a little when I get in and see the task ahead; I'm quite sure it'd be the same in an office if I had that problem. That can just as easily be the point of this sort of action.