Your basement flooding probably has nothing to do with the septic tank. The cracked and bowed wall is a concern. The cracks are probably the cause of the flooding, and the bowing is probably the cause of the cracks. Don't spend a cent on repairs until the cause of the bowing is determined.
Possible causes of bowed walls:
1. Hydrostatic (water) pressure in the soil outside the wall
2. Tree roots growing into the wall
3. Insufficient wall thickness for the height of the wall
4. Insufficient reinforcing in the wall
5. Failure to brace the top of the wall into the floor structure
6. Improper backfill (stumps, rocks, clay, debris)
Your bowing could be caused by any one, or a combination, of those factors.
First step is to find out why the wall has bowed. This may involve some professional advice, and possibly some excavation outside the wall. Once you know why, you can remove the cause, repair the wall, and waterproof it on the outside. There is nothing you can do inside the basement that will solve the problem. The problem is outside, and so is the solution.
Architect (NY) and Home Designer (PA)