If there's not much else "wrong" with the property (or if it's relatively new), you might choose to go ahead and pay a plumber to get it over with.Definitely use polybutylene pipes as a "negative" when negotiating the purchase price.With inflation, tradespeople retiring, and the growing population moving to the area, it might well be less expensive to have them switched out sooner rather than later. 

If he plans to live another 50 years, he needs an inflation adjusted way to protect wealth. 

Unless there is a crazy year of inflation, this is adequate rent increase.  

NOTE: Did not factor rental appreciation, property appreciation, inflation, etc. so don't beat me up on the numbers BP :) This is just to show the power of building HH stack and leveraging dept.

However I am a bit dissuaded by the level of market inflation there in the past few years.

How old are they/how much life-span is left, what's replacement costs for that today, then forward cast it, take into account inflation to such costs, now you have your total and a date.

What I see is there are many people from abroad who just want to park money here vs their home country due to inflation or some other reason who are willing to take minimal returns in exchange for principal safety. 

The prospects for appreciation are limited (probably below the inflation rate), your tenant pool sucks to manage from out of state, your risk is high because you don't know what the heck you're doing - none of us did on the first go; that's not personal - and your flippant verbiage is treating this more like trading stocks than buying property. 

Financial freedom requires a passive income that meets three requirements:Your income outpaces inflation: Inflation continually erodes the purchasing power of a fixed amount of money.

Buying sub to also has risk especially if the property is being sold at an inflated price due to the sub to which is the case on properties that have not sold for an extended period of time.