Water traps are used to help prevent condensation from building up in your valves or manifold. Water traps are a must for those that daily drive in below freezing temperatures.
The SMC Auto Drain Water Trap will automatically purge when the collected condensation reaches a certain level. Once the internal float reaches a certain height, the valve at the bottom of the trap will open and the pressure from the tank will cause the condensation to purge automatically. It pretty much works like a toilet.. for your air system.
Since this water trap drains automatically, you will need to ensure that you have air line running from the 3/8" PTC port on the bottom of the water trap to the outside of your vehicle. The 3/8" air line is not included with the trap so you will need to purchase that separately.