Hi Elvis,
The other port is for draining water.
You can connect this port with a drain fitting,
such as the BPTA-EFW-V2-GS or a valve.
If you have questions, feel free to contact us.
https://shop.bitspower.com/index.php?route=product/product&product_id=7286&search=exhaust&page=2
https://shop.bitspower.com/index.php?route=product/product&product_id=6820