One time.
 

I witnessed "knocking" at a gloryhole one time and there wasn't any filming going on. I was spying a guy sucking a huge, perfect cock through a gloryhole and after watching him suck, lick and slobber all over that curved monster for a while I heard some knocking coming from the other stall and the guy sucking went down on that cock as far as he could. At first, I thought he was just seeing how much of it he could take at one time and then I thought I noticed him swallowing. Shortly thereafter, the cocksucker pulled back and I spotted some cum dribbling from his chin as he tugged on and then licked a bead of cum from the retreating cock. Maybe it was something they had worked out in advance, hard to say I guess.
If I'm sucking your cock, though, you don't need to knock. I want you to feed me your entire load, it's what I'm there for. :D

Well, seems like all aspects of this subject have been covered here - - and I wanna add my $ .02 worth. It wouldn't bother me if someone did. I think it's kinda cute that he wants to be courteous. It's a fact that a seasoned cocksucker knows when he's bout to get his warm, creamy reward. The donor usually pushes it all thru the gh as hard as he can . . . the shaft stiffens and the head swells . . . more often than not - the donor will grunt or moan - but, not always. I love when he talks dirty like . . . "You hungry? dinner's served" . . or something similarly HOT.

i'm with bjbud. one hot time, a guy said, "better be thirs(ty)... oh, uh, uhhh, drink it, drink it, oh fuck yeah, drink me!"

I don't knock but I try to cum as hard as I can as a way of saying thank you .

yes please!!!

Much appreciated - my man. Can't think of a more thoughtful way of sayin "Thanks"