The stack is cast iron.

With that being said, I prefer to buy vacant units so I don't have to terminate leases or drastically hike up rents upon purchasing a place, not to cast judgement on those who do so (a lease is a contract, once that's fulfilled you don't owe the tenants below market rent, nor should they expect that), but that is my personal preference.

He found that the cast iron under the basement has some corrosion and would probably need to be replaced as another blockage would probably happen.

This is the concrete product cast  on the upper floors of apartments.

@Coury Cast - thanks for the this info.

Upgrading things like cast iron and galvanized plumbing and wiring can get expensive so always consider that when searching for properties.

When you are shopping for your replacement property you will want to cast a wide net.

A refrigerator can cast $1,000 or $10,000.  

I would also want to vet their team (lawyers, CPA, lenders, PM, etc.) a strong supporting cast can compensate for a lack of direct experience.Do they have skin in the game?

The upside is that you can cast your net wide, however, the downside is that you've got multiple state licenses that have continuing education (CE) requirements and of course costs of joining local boards, etc. depending on whether their in very different locations.