I bought masses of facecloths, flannels because I presumed clients would use them on their cock n' crack in the shower.
But when I offer they look at me like I'm a martian. "It's to wash with'. Blank face. Then they refuse, there's no thinking about it for a second.
No one has ever requested one either.
So now I have boxes of them.

If I'm doing rimjobs I personally give that soapy flannel an outing and jam it up there for a good few minutes.