A window sill pan flashing or a door sill pan flashing with drain. The sill pan flashing has an inclined base, and window or door continuous or near continuous sill supports which can be extruded as part of the base unit. Sill pan flashing offsets provided in the rear sill pan flashing wall and in the front flange create a flow path for water to drain from the sill pan flashing to the exterior of the building. The base may be solid or hollow with window or door supports extending vertically through the base. Extension couplers are provided to join a plurality of sill pan flashing base sections. The sill pan flashing base sections and extension couplers may be manufactured by extrusion.