During the rehab, pipes leaked and had a well-known plumbing company came out 3 times for fixes.

We installed a new roof, new flooring, lighting and plumbing fixtures, resurfaced countertops and painted the walls and cabinets.

However I know nothing about plumbing/mechanical and seeing the back room was daunting.

Unfortunately, I do not live in a market where house hacking is easy to do but my ideal house hack would be an ugly 2-4 plex built after 1978 with good electric and plumbing. 

I did the math and realized that even a total overhaul of the plumbing system in the house would still allow for this deal to work so I pursued it.How did you find this deal and how did you negotiate it?

You will need to comply with local construction laws including well water if there is no city water, plumbing, electrical, sewer, and wind resistance.

The home needed foundation and plumbing repair which shot up the repair expense.

New roof, foundation and plumbing.

Part of the reason is that, you need to reconfigure the whole building from plumbing, walls, electrical, etc.

Keep emergency contacts for HVAC, Plumbing, Electrical3.