We had this same issue every spring with our first house. There was no way the previous owners didn't know about this.

Black mold... Be very careful with that. If you breath it in you will get sick!

I hired a company to come in and remove the black mold from our basement. Before we moved we had the main drain line going to the city plumbing replaced because it was no good. This is why we were getting water in the basement because melting snow was able to flow into the pipe and into our basement drains. Our basement bathroom is where we would snake to the main line and pull out many roots.

I couldn't leave the house like that to the new owners like the previous owners did to us. So I spent the 10k to get it fixed. They ripped up the driveway and part of the front yard to fix all of the plumbing coming from the main line under the street going to the house.

But, yeah. I would have professionals deal with that black mold. You don't want to be anywhere near that shit!!!