Put on pants, a long-sleeve shirt, work boots and thick rubber gloves. Put on a pair of rubber waders.
Turn off the gas and water lines -- including pipes to and from the water heater -- in the basement.
Open all the windows and doors in the basement to help with ventilation. This also helps dry the basement. Remove all items from the basement.
Remove the sewage from the basement with a wet vac. Regularly discard the contents in the wet vac’s canister in a toilet.
Rinse the walls and floors of the basement with a water from a hose. Use the water hose pressure to direct the water toward the drain.
Add 2 cups bleach to 2 gallons warm water. Stir the bleach and water with a spoon. Saturate the bristles of a brush broom in the mixture.
Scrub the basement walls with the broom and work your way down to the floor. Saturate the brush broom in the mixture when needed and continue scrubbing until you have cleaned the walls and floor.
Rinse the mixture off the walls and basements with the water hose, directing the water toward the drain. Discard the mixture down the drain and rinse the bucket and brush broom clean.
Repeat the scrubbing process. Let the basement air dry.
Rinse items you previously removed from the basement with a water hose to rinse off sewage. Launder washable items as you normally would. Discard non-washable items that encounter the sewage.