> I doubt a tourist submarine, or really any submarine going to this depth, has multiple compartments

Indeed, from their website: https://web.archive.org/web/20230613051805/https://oceangate...

"Is there a bathroom on the sub?

There is a small toilet located in Titan’s front dome – it doubles as the best seat in the house. When the toilet is in use, we install a privacy curtain between the dome and the main compartment and turn the music up loud."