The correct answer is: A. 3 years.
Septic tanks are designed to treat wastewater from homes and businesses. The tank holds the wastewater while solids settle to the bottom and liquids rise to the top. The solids decompose over time, and the liquids are discharged into a drain field.
The sludge from a septic tank should be removed every 3 years, or sooner if it starts to build up too much. If the sludge is not removed, it can clog the drain field and cause problems with the septic system.
Option B is incorrect because 3.5 years is not the recommended maximum period for removing sludge from a septic tank.
Option C is incorrect because 4 years is not the recommended maximum period for removing sludge from a septic tank.
Option D is incorrect because 5 years is not the recommended maximum period for removing sludge from a septic tank.