They probably only had sex for a few hours at the most, the urine likely didn't go bad yet, plus it's diluted. And you're right, I just always assumed bathrooms smelled bad because of #2 (but I've never really experienced how urinals smell since I'm a girl, but girls are pretty bad in terms of bathroom smell). Nah, I know urine is dirty and can lead to bad bacteria and infection if left to fester for a few days, but I'm sure all of us have slept more than a few hours on beds with pee on it when we were children. They probably cleaned up immediately after DG was done with Jiwon's shit.
It was so freaking sexy until DG took a piss. I get that some people thought it was hot, but they literally slept in piss, I can't imagine how horrible it must have smelled.