An anti-siphon drainage device having a housing forming an internal chamber, an inlet and outlet ports part of the internal chamber and fluidly connected by a primary flow path. A valve seat is associated with the primary flow path, a sloped section extends from the valve seat, and a valve element disposed in the sloped section and can seat in the valve seat to restrict a fluid flow into the primary flow path from the inlet port. A secondary flow path can have an opening near the inlet port and an orifice near the outlet port. A regulator has an aperture to selectively open and close the opening of the secondary flow path. When the valve element is seated in the valve seat and restricting the fluid flow into the primary flow path, the fluid flows into the secondary flow path.