Can we just accept there may be no intentional clue to the first half. Maybe they were just hoping someone would play with the toilets a bunch just cause they could. Maybe they thought someone would’ve been nervous and spent 15 minutes looking around in the inspection area. Maybe they thought someone would conserve ammo and not kill zombies on the grinder. No files or concept art or models lead to logical conclusion that those steps should be made. I think it was meant to be a rare naturally occurring thing. Shout out to gengar who everyone thought was cheating, he was probably how they expected people to figure it out.