Bathroom sink and tub drains are often clogged with hair, foreign objects, or soap, shampoo and conditioner buildup. Over time, the gradual accumulation can lead to a slow or completely blocked drain.

Clogged toilets may be due to toilet paper overload, or an object that may have been dropped into the toilet.

Incorrect pipe installation could be a problem. 

Broken pipes could be the cause of a blocked drain. Pipes can break from age, tree roots, or improper installation.

The fall or slope of a pipe is crucial to proper water and sewage flow. Drainage is directly related to gravity. Without enough fall on a pipe, it can become clogged and worsen until total blockage occurs.

Sewer lines can be blocked by root growth in the pipes, sewage buildup, sinking or bellies in the pipe, or from cracks / breaks. ​