Water softner brin line ?

[DJDailey]

I bought a house with a twin softner set up. One tank is a 9x48tge other is a 10x54. Both tanks have a BNT 1650F control valve on them. However only the 9x48 has brine line on it. The other has a connector not going to anything and when I started the regen/backwash you hear it sucking air. Both tanks are connected to each other. I took the brine line off the 9x48 and put it in the 10x54. To see what happens. Is this a normal setup?