sticks up a couple of inches over the grass in the back yard. It just does straight down into a T joint in the main sewer line about 2' underground.

The other day I accidentally hit it with the deck of my riding mower, and the cleanout is now loose - it looks like it cracked the PVC at the base of the T joint. Because I'm on a septic and not on city wastewater, I'm a little concerned that this could lead to rainwater or even dirt/mud or other debris making it into the septic system and increasing the maintenance costs and frequency of pump outs.

My first reaction was to dig down and repair the crack with some waterproof tape or something. The sewer line isn't under pressure, and so a crack at the top of the pipe in the joint shouldn't impact anything, and some tape would seal it up and prevent dirt and rainwater from intruding into the pipe. And if I pack dirt around the pipe, it shouldn't move and impact that seal from the tape.

But I'm wondering if there are any other considerations I need to have that would necessitate digging even more, cutting the whole T joint out and gluing a new one in so that it's all secure. That doesn't sound like a fun job, and I can't think of any reasons why it would be needed, but I may be missing something.