[Rust-O-Matic]

Hey fellas, I just rolled out from under my '95 suburban again, and have a question. There appears to be two 1/4" brake lines running along the driver side frame rail, one of which is way rusty and leaking everywhere. I intend to replace the rusted one, but what is the other one for? I haven't followed it to the rear axle yet because it got dark, so I don't know what it attaches to yet. The "extra" one (which happens to be in much better shape than the other) is spliced with a piece of rubber hose and pinch clamps toward the rear end, so I presume it can't be for pressure. And just to clarify, I'm not talking about the fuel lines that run along with the two brake lines. This may be a dumb question to someone who is familiar w this series of trucks, but I'm not. My '66s brake lines were totally self explanatory haha. Thanks!