plumbing can be broken down into several layers, incoming from water source (City, utility) to the building problems (is usually a utility problem / fix) once the incoming water is inside the building it is your problem. If the leak is above the lowest floor cement, it should not be too big a deal, unless all the old copper pipes are ready to be replaced. Sink drips, p-trap drips, faucet drips are minor in the whole house plumbing. Replacing a building wide boiler is very expensive ($10k - $20 k), hot water tank ($500- $5000) Water softeners about the same ($500- $5000).
Make sure that building managers / property managers all know where the water shut off valve is if you buy the building, comes in handy if there is a major leak, to shut off all water fast.
Dish washers, under sink leaks, faucets, running toilets, are common, should be fixed prior to any new tenants.
ON THE OTHER END of plumbing is vent pipes, and waste water pipes (mostly black PVC) carrying waist water from building to the city street sewer lines
I have heard of landlords having the entire building snaked (roto rootered out the pipes) once a year as a preventative maintenance measure, as many tenants pour grease down kitchen sinks, and wet- wipes (flushable wipes are very hard on plumbing) down toilets causing back up clogs.
Most of the leaks on the waist lines are in the p-traps, toilets, clogs in the main drain line and sewer back-ups.
Over time the waist lines (used to all be cast iron, will need to be trenched and replaced with PVC out to the street connection, as the cast iron breaks down over time, allowing tree roots to enter and clog / block the exiting waist water.
You best best is to call a local plumbing company, ( plumbing 911, mr plumber, rotor rooter) and have them come out and give a quote on repairing all the items the inspection found.
The plumbing issues on a duplex may be more manageable then say a 100 plex with a broken waste line or main water in line, but size and scope is everything. You can drop $20,000 on brand new PVC waist lines, permits, trenching, labor, and covering up the trench on a duplex, or a brand new leach field for a septic system.
