All compressors generate water. It goes hand in hand with compressing air. The better the compressor the more water created. You need to get the water out otherwise it will get pumped into what ever you use the compressed air for. Our tanks have multi ports and can be rotated so a port is at the bottom where water would sit. This unit is securely screwed into the tank (1/4″ BSP) and sealed with paste or plumbers tape. Internally it screws in and out and is sealed with an o-ring. Water escapes through the hole in the pics and out the core of the inner piece. You can attach a small bit of hose to direct water outside if the tank is inside the car.
This should be done each time your service your vehicle
The threads are 1/4 BSP which is a universal standard air fitting size.