My suggestion would be first and foremost having you trained that fuckhole is your mouth's primary purpose.
Were you my own slavegirl you would spend several hours learning and practicing the art of giving oral pleasure on a large (and possibly used) dildo before applying what you have learned to your Master, and then hold his hot semen inside your mouth while you await his instructions whether to swallow or to leak his load out over your body and any allowed clothing he chooses, as and when he sees fit to give those instructions?