Facility Fishing is the act of searching for a restroom. Facility Fishing may be done simply to find a rest room in an unknown location.
However, Facility Fishing is also performed when one seeks to find a rest room that is located off the beaten path where there will be more privacy and likely little to no interuption from others coming in while defecating. This is most often performed in large buildings and locations where there are lots of people.
Leroy was at the convention center and there were hundreds of people at a trade show. He went Facility Fishing to find a bathroom near the loading dock where he was able to take a dump in privacy without a stampede of other people in and out.
A badass research facility located in New Mexico. After a cataclysmic disaster in Sector C, Gordon Freeman is left to fight off retarded zombie alien things and other creatures. The Hazardous Environment Combat Unit (HECU) is sent in to kill anything and everything remaining, while the Black Ops are sent in to arm a nuclear device. This event leads to the Seven Hour War, which destroys most of the world's population, and leads to the events in Half-Life 2.