mouser
n.— «Over the weekend, 32-year-old Michael Krube was arrested for trespassing in the St. Paul city sewer system. He’s known as a “mouser,” a slang term for a group of risk-takers who explore caves, tunnels and sewer systems.» —“St. Paul Police Battle ‘Mousing’ Trend” in St. Paul MyFox Twin Cities (St. Paul/Minneapolis, Minnesota) Jan. 13, 2009. (source: Double-Tongued Dictionary)