A sewer line that has deteriorated so badly that portions of the pipe have eroded away, resulting in a tunnel through which shit flows. These unique habitats may be home to the endangered sewer horse. The word is a portmanteau of shit and tunnel.
You can smell the shunnel every time it rains. We should probably replace the pipe, but it's critical sewer horse habitat.
by TheSilentLifter July 14, 2016