Backed up basement floor drain
About 2 months ago, I had a busted pipe outside leading to my septic tank. I had it fixed, but since then, we've had 2 heavy rains, and both times water has backed up out of the basement floor drain, flooding the basement. I thought maybe something had gotten stuck, but when I poked around, old black sewage sludge came up out of the trap. The water receded very slowly after it stopped raining--except for this time it didn't recede at all. I was worried the problem was related to fixing the septic pipe.
When I fixed the sewer pipe, I patched the hole where the pipe entered the tile septic tank with concrete. It wasn't completely enclosed before I fixed the pipe. But I figured I needed to enclose it because I was getting backflow when I flushed. Now that it is enclosed, there's no where for extra water to seep out when it rains heavily causing the water to back up into the basement drain. Am I correct in this assumption? If so, what do I need to do to correct it? Does it mean my septic needs emptied? Or do I need some type of back-up valve installed. Or is there something else going on?
What's the best way to determine if the floor drain is connected to the sewer? By the way, this house was built in 1953.