We used a test set at the central office that would test pair gain/loss on a dry pair. It also could send talk-battery on a long loop to communicate with tech on other end. Can not remeber the brand, but it was used for central office applications to remote sites.

Worked like a champ. We had squak box at central office end and tech on other end used there buttset.

Good Luck!!

If all else fails, use a BFH.