What causes the main line to back up?

There are many things that cause a main line to back up. Some of those could be a belly in the line,  roots, bad glue joints, burrs from a cut pipe, no fall in the line, or foreign objects in pipe.

What is a belly in the line?

A belly is any lower portion of a drain line that holds small or large amounts of sewage. This will cause any solid that hits the belly to slow down or stop causing a stoppage or slow drain.

How do roots cause a main line back up?

Roots get in the pipe at any connection point. As the root grows inside the pipe they will begin to catch solid objects and hold back the proper flow of the drain.

How can bad glue joints effect my sewer line?

A bad glue joint results in a poor connection for the pipe. This poor connection leaves room for roots to grow, cracks to form, or if the pipe separates- accumulation of solids.

What is a burr?

A burr is any unsmooth area of cut pipe. This jagged edge can grab onto toilet tissue and other solids to prevent them and things behind them from moving down drain line.

What does proper fall in the line mean?

Proper fall means when a level is placed on the pipe there should be a 1/4” to 1/8” fall on 4” and 3” pipes and 1/4” fall on 2” pipes angled down until the city connection point. If this proper fall does not exist you can have backups from improper flow.

What foreign objects should not go down the drain?

Anything beyond human waste, toilet tissue, and the small scraps you put in your garbage disposal.
See these two links for more explanation of why check out these other blogs below.

https://www.jdprecisionplumbing.com/what-can-i-flush-down-the-toilet/

https://www.jdprecisionplumbing.com/what-can-i-put-down-the-garbage-disposal/