When I was stationed in San Diego back in the 90s there was a barracks I lived in temporarily that we were told was supposed to be condemned for various reasons but was left open for years, as overflow. I don"t know if that was true, but I know you could tell when someone would flush a toilet in the building because a massive wave of cockroaches would emerge from the manhole cover behind the building, only to recede back in a few minutes later. We tried not to think of the physics of how many roaches must've been in there for that to be necessary.