I have found a couple properties like this in the last couple years. The worse I have found though was a property that had the main mounted at the main house. The line then went into the basement and was Tee'd off. One of the lines went back outside to feed the two garages and six rental cottages. The line that went outside was Tee'd underground to go to each of the eight buildings. After a day of potholing and not getting any further ahead, we decided it was cheaper & quicker to have a plumper just disconnect the outside line, if we hit anything we would pull new lines for him. Thankfully we somehow made it trough the whole job without hitting a single line.