Sewer and water piping and cause for upgrades due to adding a new unit?

Food can clump together and cause clogs.Facial Cleaning Pads – Thicker than toilet paper and thus can cause problems.Dental Floss – NOT biodegradableHair – Clogs pipes in no time.Dirt – Dump it outside, not in the toilet.Dryer Sheets – Made out of synthetic materials, not biodegradable.Prescription Medicines – Destroys bacteria and contaminates groundwater.

But I'm a little hesitant to take out the sink because it's a very old setup under there (as you can tell by the copper water pipes).

-There is a vent just above the stove, on the wall left of the stove (you can't see it in the picture) which I believe is supposed to be for exhaust from the stove, but it does not have a fan in it.

There is lot of work to be done when you have to fix a pipe leaking into the foundation.

Such as, condo fees usually cover roof, R&M exterior (lawn, their side pipe burst, etc.

From what I understand, the mold has taken over a wall in the living room, which says to me there's a leak in the bathroom pipes on the other side of that wall.

This is a first floor condo and We found out the common drain pipe that ran under the concrete right under our living room had deteriorated into nothing, so all of the drain water was coming back up through our drains!

@Mariah Porter I've lived through some pretty serious basement flooding issues on one of my own rentals, so I definitely feel your pain--it's not a fun situation.My natural reaction was also to wonder about the seller's disclosures, and whether I could bring a lawsuit against the sellers, but I pretty quickly realized this wasn't feasible or advisable (in my situation, it would have been almost impossible to prove the sellers were negligent or withholding a disclosure, and the legal fees would have been steep). ...but, I'm not a lawyer, so it may be worth asking a lawyer anyway...I think your first priority here is to figure out what's causing the flooding, and fix that issue as soon as possible.Most houses have a drain at the lowest part of the slab that's intended to collect water in event of a flood (for instance, if a broken pipe caused a flood)--I assume that that's what this pipe is? 

Must 1958 houses have cast iron pipes and wire is outdated.