Newbie closing on first deal in 2 days- Issue with owner repair

[Nick D.]

So I have a 6 family under contract in New Britain, CT that I am expected to close on in 2 days and I have scenario at hand with the sewer/basement. After going through the inspection stage I asked for some repairs to be made, some mold to be removed and the sewer in the basement to be unclogged since it was a bit backed up. The owner agreed to fix everything and did send me invoices but when I did a re-inspection after the repairs, me and the realtor noticed the sewer leak was now even worse than before.  We are expected to close in 2 days and I'm a bit worried not only about the owner having to fix this issue, but in the event of future damage now that about 1/4 of the basement is now flooded and the leak is now coming from what looks like one of the units on the first floor. Basically what I wanted everyone opinion on is, say the seller fixes this issue, what can I do to assure this issue is fixed properly. My concern is the seller said this leak was fixed from the sewer, and now there is a leak coming from one of the first floor units, re clogging the sewer in the basement. I will go walk through the building on the day of closing, but say in the event the seller does a quick/cheap repair and the leak reoccurs just days later, I don't want to be stuck with a sewer/plumbing bill right out of the gates with my first deal.

How can I make sure these repairs are handled properly and do i need to add in additonal language to the Purchase Agreement to better protect myself in the event this sewer clog/leak happens again shortly after closing on the property.

Thanks