Use your mouth...

You look around to find any tissue so his cum would not just fly everywhere and all over your carpet, if your parents ever finds out, you will be in huge trouble, you remembered that there are some tissues in the bathroom, but that's a bit too far.

You couldn't stop jerking him off, because that would be mean, running out of ideas, you did the only thing you could at the moment.

You suck his cock, and the moment he saw and feel the softness your lips and the warmth of your tongue touching his cock, he got turned on so much that he cums immediately, and his cock exploded in your mouth, pumping so much cum inside.

Oddly it didn't taste that bad at all, not as bad as you would've thought anyway.

"Holy crap... sis... did you just let me cum in your mouth? That is sooo hot..." He asked, still not believing what just happened.

You just nodded at him still with your mouth full of his cum.