People who take it in the ass with any frequency often "get in tune" with their body enough to know how clean things might be at any given point. Cleaning out for anal doesn't have to be a huge chore. Sometimes a good shit and a douche to rinse out are plenty.
In the OP's case, the dizzy bitch oughta had the courtesy to at least go to the bathroom before she invited him to ream her drainfield of love