Toilet Leaking

Last week discovered that my 1st floor bathroom's toilet is leaking. With having an unfinished basement I located the toilet and found the leak was coming from the closet flange. I pulled out the toilet and the tiling and realized that I'll have to replace about a 2 by 3ft section of the sub floor.

With research I found that the toilet flange is glued to the sewage piping below the floor and will have to cut out the sub floor very carefully not to damage the flange or go downstairs and remove a section of the sewage pipe, which will allow me to remove the closet flange.

I believe the easiest solution would be to cut out a section downstairs and install a new flange once I put in the new sub floor.

Questions I've never worked with the septic system. Anything I'd have to look out for or do before cutting the line. Will this be as easy as I'm imaging it to be? The area I'd cut is independent of other lines. So I believe nothing will run out when I cut it?? Just a gravity septic system.

Thanks for the help

It would be easier to put a Flange extender in, then try to cut out the old and refit.

When installing a toilet flange, ideally, it is installed on top of the finished floor, and anchored through it into the subflooring. If the subflooring needs to be replaced, install the new flooring, retile, (you can notch the tile so you don't have to drill through them), then install the new flange.