A controlled flow drain having an upper flange coupled to a lower flange. The upper flange defines an inlet cavity and the lower flange defines a swirl chamber. The inlet cavity and swirl chamber are in fluid communication via a swirl nozzle defined within a swirl nozzle plate that separates the inlet cavity from the swirl chamber. After separating debris within the drain fluid, the drain fluid is accelerated through the swirl nozzle and discharged into the swirl chamber, and more debris is thereby separated and eventually settles into an annular groove. The drain fluid may then exit the lower flange via an exit control passage. The swirl chamber may be flushed with a series of flushing liquid injection ports symmetrically-arrayed about the annular groove. Flushing the swirl chamber removes fluidized debris and also remove any built up fouling present on the swirl nozzle and exit control passage.