Clean as a slip

When you take a big shit and you go to wipe but when you look at your toilet paper after the wipe there is so shit streaks on it. So your butthole is as clean as a white slip.

Also known as the "clean slide"

The result of taking a tremendously fat shit, that was both sinfully delightful, guilty, odifourious, shameful but gratifying, but not needing to wipe a second time because it left no evidence.

also associated with "riders block" the condition in which riding a bicycle, motorcycle, horse, personal watercraft, or any activity that entailed prolonged impact on the buttocks, and delays defecation.