I know this in in the archive but I just had a rather interesting thought.

there is a dom who says that at the end of a blowjob he pees in the subs mouth instead of cumming.

If I am remembering my biology right that is impossible.

1) Human reproductive systems want to do only one thing...reproduce.

2) When sexual stimulation is being given the waste disposal system is shut down. Our biology does not want sperm contaminated with piss.

3) If he is getting a bj, his urinary equipment is temporarily shut down to allow the delivery of clean sperm.

So,

Changing right at the last second is not possible. In fact when oral stimulation gave him an erection, his urinary system is already on standby...

Therefore

His OP is a work of fiction.