Which of the following is a common cause of a clogged drain?

Excessive grease buildup is a well-known cause of clogged drains. When grease, fat, and oil are washed down the drain, they can cool and harden, creating blockages in the plumbing system over time. This buildup can combine with other debris, such as hair, soap scum, and food particles, exacerbating the clog and leading to poor drainage or a complete blockage.

The other options relate to good practices or products that typically help prevent clogs rather than cause them. For example, using a water softener can actually benefit plumbing by reducing mineral buildup, while the proper disposal of waste and regular maintenance are both crucial practices that help keep drains clear and functioning properly. In contrast, allowing grease to accumulate without proper disposal and management is a primary factor that increases the likelihood of experiencing a clogged drain.