With some septic systems electricity is needed to move along the treated water and spray like a sprinkler to empty the last of three tanks. The solids must get pumped out when needed, depending on amount of use. Last year when Hurricane Ike hit us we stopped using the toilets because the elec. was out for days and couldn't empty the cleaned water. Toilet will flush just fine and gravity works to empty into the septic system; the problem is it can't pump the water out and would eventually fill up. So we just played camp out. We live in the woods so DH had a great time marking his territory!