The McAlpine Waste Valve 1.1/2" Uni Macvalve-2 is a plumbing fitting designed to control the flow of waste water from a sink or basin. It prevents foul odours and gases from entering a room by creating a seal. The valve opens under water pressure to allow discharge and then closes to prevent backflow. It can be fitted horizontally or vertically and is ideal for installations where a non-return valve is beneficial. This model features a BSP female inlet nut and a universal compression outlet. Available in 1.25" and 1.5" sizes.