Our plumber guy clued us in to a gadget that lets you clear the clog yourself *IF* the clog is between the cleanout and the septic. Call a plumber if the clog is between the house and the cleanout. You'll know which scenario you've got when you take the lid off the cleanout: Between cleanout and septic will result in overflow of water gushing up. If between house and cleanout won't have a welling up of water because the excess water in that line drains to septic.
The product is the 2.5" or 3" DrainJet Hydraulic Drain Flush, which is an expandable bladder that fits onto the end of your garden hose. Snake it down into the tube as far as you can and then turn on the water. The bladder expands to create a seal and the jet of water and pressure blasts the clog into the septic. (Make sure it snakes towards the septic, otherwise you might destroy your toilets.)
Costs about $55. Plumber is $180-$300 to clear the line dependent on time of day and what day of the week.
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