Why is biodegradable toilet paper blocking drains?

Biodegradable toilet paper will block drains because it takes weeks, sometimes months, before it degrades.

One of the issue being encountered is that drain lines to sewers are not in the majority smooth . They frequently, especially in older buildings have cracks, slit joint seams etc . When any tissue is flushed through there is a tendency for some snagging on sharp edges of the sew line to occur as more and more paper is disposed of it can build up on the "construction". In addition people have a habit of washing down sink units, which do eventually merge with sanitary waste copious amounts of fat. This can impregnate the paper adding to buildup. The building up of off blocking waste occurs substantially faster than the degrading of the paper which eventually can block drainline to the main sewer system. In some large towns and cities eben large sewer lines have to be manually dug out to assist in the flow of waste. There are also other disposed of materials that add to the issue such as skin wipes, cotton ball wipes used in cosmetic removal sanitaryware.