Okay stop wanking, you're hard enough now.
Grab that glass again. I want you to slide your cock into that piss. Is it still warm? Does it feel good? Slide your cock in as deep as you can but don't spill any. Slide it slowly in and out of the glass, pretend you're gently fucking it. Make sure your whole cock is covered in piss. See if you can get your balls in there too!
Thats enough, take your dick out now. Set the glass down and start wanking again. Does that feel better now that your dick is all nice and wet?
Hold that shit up close to your face while you wank. Keep going till you need to stop again. Show me how long you can last this time...