Replace your old or leaky taps with this 3/4" thread Cask Doctor Tap, which has been specially designed with a built-in non-return valve to prevent disturbances in the cask caused by beer flowing back through the tap. This can be especially helpful on very long runs, or if your beer engine's non-return valve is faulty. The plastic faucet is tapped through the cask's keystone with a rubber mallet and attaches to the beer line using a tail, nut, and sealing washer.