Congrats on your new to you Airstream. I have a 1986 25' Sovereign
. The layouts are probably similar. There should be 4 connections to the fresh water tank: 1) the fill hose (big corrugated thing), 2) a vent hose, 3) a drain hose (or pipe), 4) supply pipe to the fresh water pump.
There's also a fresh water connection for "city water" supply that should bypass the fresh water tank. Mine connects on the street side near the bumper. I say "should bypass…" because sometimes owners will build in a valve and pipes to fill up the fresh water tank from the city water supply.
I've spent a lot of time the couple weeks working on my plumbing system. If you post pics about your specific questions (and if our layout are similar) I might be able to help more.