[400TT]

Yes, that bottom connection is the atmospheric vent.

Connect a hose to it that has a bit of length to it to stop ingress of water and moisture. Do not loop or run the hose up hill.

It is good practice to make sure the bottom of that hose is protected by/up above the chassis. This reduces the likelihood of the bottom of the tube being damaged or caught/snagged by speed bumps, debris etc. As Sideshow mentioned that is why a lot of factory cars run that hose into the chassis or under body panels.

Craig White