I play assistant to a senior member of the crew and had quite a good experience. The 2" main coming out of concrete floor in the parkade had a gate valve (open) followed by a back-check valve. We replaced the backcheck and a couple of nipples between the BC and the union with a ball valve. The inner pipe was heavily corroded, maybe loosing 1/2 it's internal diameter (in 35 yr old building). The 'fun' came as the galv-pipe entered the boiler room and switcheds to copper. The last length of galv pipe (approx 3ft) was good on one end (the 90 it came off at) but a 1/4 of the threads had erroded away at the copper connection. (What type of die-electric fitting should you use for galv to copper). We just replaced and re-soldered. The rest of the day was replace toilet tank float-valves and stops in rental suits.
Sorry, no photos. Totally forgot about until the end of the day.