By taking a leak

You turn the tv onto some mindless Saturday morning cartoons, just to distract you from the slow bj you are forcing your sister to administrator. Forcing yourself to drink almost half of the water your mother left with you before leaving.

"OK Andrea, I will not be able to cum until I take a leak, and as you know I can't give permission for you to remove your mouth from around my cock until the end of the day, so guess you are going to just have to drink it all down. So for now you can stop the 'relaxing blowjob' and get my cock just inside your lips and I'll do my best not to fill your mouth to quickly, don't want you to not be able to taste every second of what is coming."

Andrea grabs the notepad and pen you had your mother bring over, and quickly writes as she complies, 'I can't believe that you need to piss in my mouth to cum.'

"What is that old dumb quote, 'Different strokes for different folks.' Seeing you with your mouth around my cock, knowing that you wont remove it until I give you permission, is a huge aphrodisiac. Ohhhh"

You manage to control your stream so that it comes out slowly and doesn't blast the back of your sisters throat and cause her to ****, but your new favorite urinal is taking it rather well.

Right as you finish and are just about to have one of your classic pea shutters, Andrea licks the underside of your cock, and you dump a second load of cum into her mouth for the morning.

As you look back down you see her holding up the notepad again with, 'So what's next?'