Before starting any work, prioritize safety. Put on your full Personal Protective Equipment (PPE), including safety goggles to protect your eyes from splashes, heavy-duty waterproof gloves to protect your hands from sewage, and either old clothes or a pair of coveralls. Ensure you have read the operating manual for the motorized drain auger you have rented. Position the auger on stable, level ground near the cleanout. Lay down a large plastic tarp around the cleanout area to catch any spills and make cleanup easier. Have several large buckets ready to manage any wastewater that may flow out when the plug is removed.

Locate the main sewer line cleanout. This is typically a 3- to 4-inch diameter pipe with a screw-on cap or plug. In this case, we are assuming it is located outside the house, close to the foundation. It may be at ground level or sticking up a few inches. Clear any dirt, grass, overgrown plants, or other debris from around the cleanout cap so you have a clean, safe working area and can get an unobstructed grip on the plug with your pipe wrench.

Position yourself uphill or to the side of the cleanout opening, never directly in front of or below it. Place a large bucket directly under the cleanout opening to catch initial backflow. Using a large pipe wrench, fit it securely onto the square nut on the cleanout plug. Apply steady pressure to turn the plug counter-clockwise. It may be very tight. Once the plug begins to loosen, unscrew it the rest of the way slowly by hand. Be prepared for wastewater to gush out. If it does, pause and let the pressure release and the backup drain into your bucket(s) before fully removing the plug. This step is critical and can be very messy.

With the cleanout now open, select an appropriate cutter head for the auger's cable. A spiral or 'retrieving' head is a good general-purpose choice for starting. Attach it securely to the end of the cable according to the machine's instructions, often using a small pin or screw. Carefully begin to feed the cable by hand into the cleanout pipe. Keep pushing it in until you feel resistance. This resistance is likely the clog. Once you've located it, pull the cable back about one foot to give the cutter head space to work effectively.

Position the motorized drain auger so the cable can feed as straight as possible into the pipe to prevent it from kinking or binding. Ensure your safety goggles and gloves are securely on. Set the machine's directional control switch to 'Forward'. Place your foot over the pneumatic foot pedal but do not press it yet. Firmly grip the cable with your gloved hands a safe distance from the pipe opening. Press the foot pedal to engage the motor and begin rotating the cable. Slowly and deliberately advance the cable forward into the pipe. Do not force it; let the machine's rotation and the cutter head do the work.

As the auger cutter head encounters the clog, you will feel the cable tense up and the motor may strain. This is normal. To effectively clear the blockage, use a back-and-forth motion. Advance the cable a few inches into the clog, then retract it slightly, allowing the cutter to break up the material. Repeat this process. Listen for changes in the motor's sound and feel for a reduction in resistance, which indicates you are breaking through. Once you feel the cutter pass through the main obstruction, continue to feed the cable another 10-15 feet down the line to ensure the pipe is fully cleared of any residual debris. If you pull the head back and it is covered in tree roots, you've found the common culprit.

Once you are confident the line is clear, it's time to retrieve the cable. Switch the auger's directional control to 'Reverse'. Activate the motor with the foot pedal and carefully guide the cable back out of the drain and into the machine's drum. It's highly recommended to have a garden hose with a spray nozzle ready. As the cable retracts, spray it down to clean off the sewage and debris, which makes cleanup much easier. After the entire cable is back in the drum, test your work. Run the garden hose at full blast down the open cleanout pipe for 5-10 minutes. Then, ask your helper to go inside and flush a toilet and run a sink simultaneously to confirm that the drains are flowing freely and not backing up.

With the line confirmed clear, the final step is to seal the cleanout and clean your work area. For a better seal and to make future removal easier, wrap the threads of the cleanout plug with three to four layers of Teflon tape in a clockwise direction. Screw the cleanout plug back into the pipe, starting it by hand to avoid cross-threading. Finish tightening it with the pipe wrench until it is snug. Be careful not to overtighten, as this can crack the plastic fitting or pipe. Roll up the plastic tarp, ensuring any mess is contained within it for easy disposal. Dispose of soiled rags and gloves. Thoroughly clean any rented equipment according to the rental company's instructions before returning it.