Okay, so Zack, Nick, and Aaron spends an entire night being locked in a haunted building. Question: Do they go to the restroom at all during that whole night? If they're exploring a haunted hotel or resturant, do they just quickly zip to the boy's room during the investigation? Also, what about places that have no visible sign of a working restroom. Do they just run out to the brush and go?
My guess is that the trio do their "dirty work" away from the main area, and just make themselves "purged" before the lockdown. Helps with not only leaving the unsavory bits out, but also potentially prevents Bring My Brown Pants.
IIRC, it was mentioned exactly once. At the first Bobby Mackee's investigation, Nick was apparently bothered by something unseen while at the urinal.
Two mentions now, with Zak commenting in the Winchester Mystery House that the bathrooms seem to be there to tease the living, not the spirits. The tour guide tells him matter-of-factly that the house doesn't have running water, and he'll have to go outside (if he can find the way out, anyways).
As an addition to the above mention of purging beforehand, they spend an entire night, roughly nine to ten hours, at a location filming, which they then have to cram into an hour-long program that devotes about half of the episode a history of the location that they're visiting, leaving roughly thirty minutes for the actual investigation. They're going to be cutting out unnecessary bits like bathroom breaks just to be able to condense the investigation down to fit the time frame they have to work in.
During the investigation of the Winchester Mystery House, Zak himself said, "I would rather be locked down in locations with asbestos pouring out of the walls and into our lungs than be teased to use the bathroom TWICE!"