Help - Rental Plumbing Issues - Cost Benefit Analysis

[Kristofer Kohlstedt]

situation: we have a duplex that is experiencing plumbing issues on the front unit. We have had three plumbers out to work on unclogging the pipes and we have also replaced a section of the pipes. Now, we are still having issues with the line getting clogged. We have had someone come out with a camera and he recommended we replace the remaining cast iron pipe from the front unit ($800-1600). We had another plumber come out and he recommended us replacing the mainline. the washout is under the driveway so the normal $3k mainline replacement is now $7-12k due to jackhammering the driveway. 

we have heard different things and we are seeking to be effective with our expenses as $7-12k is a pretty hefty expense that we would prefer not to pay if we don't have to. The other thing I began asking myself is well what is the opportunity cost of selling the duplex and putting the money into another investment. we have about $50k equity in the duplex as it sits now. we enjoy the cashflow ($500/mo) from the duplex but does the cashflow justify the cost? it would be over a year to recoup our investment in the mainline replacement and as a conservative person, I am also considering some additional expense to come up in the normal course of life and we need to expense something else. so I'd say 2-3 years before the property is profitable the way it operates now.

Open to hear thoughts and feedback on my approach as well as experience someone has had with rentals/plumbing. Thanks in advance.

Kris