 Trench drains are commonly confused with French drains, which consist of a perforated pipe that is buried in a gravel bed, and which are used to evacuate ground water.A slot drain, also wrongly associated with a trench drain, consists of a drainage pipe with a thin neck (or slot) that opens at the ground surface with sufficient opening to drain storm water.There are four common types of trench drains which are based on forming or installation method.