Long drain lines are problematic, especially as they service kitchen sinks. For more than a few reasons, which we will discuss in this article, a long drain line gets clogged to the point, a cable will generally not provide long term cleaning. Long drain lines often must be hydro-scrubbed.
Take a look at the video below of the 60 + foot long drain line.
This is a replacement for what was originally servicing the drain. The original drain was severely clogged for several reasons.
1. The inside diameter remained the same, for the entire length of the drain.
This is a problem because, once the blockage begins building along the bottom of the pipe, the organic material will accumulate, evenly along the bottom of the pipe, in layers. This means, once the drain line stops flowing, the entire length of pipe will be clogged for the entire inside diameter. At this point, you either cut it out or hydro-scrub it. Fortunately, hydro-scrubbing is much more cost effective.
2. Another reason a blockage will occur in long drain lines is limited pitch. The pipe must fall as it runs horizontally at a rate of ¼” per foot of horizontal travel. If you are running the pipe in a ceiling below the kitchen, you will have limited space to run the piping in the joist before the pipe must drop into the ceiling space below. Building codes, plumbing codes and not being able to cut through floor joist in the top and bottom 2” of joist, the pipe generally leaves only 4” to run horizontally and drop at a rate of ¼” per foot of horizontal travel. Therefore, drain line can only run 16 feet before dropping into the ceiling. Many times, the plumber installing the pipe will allow the pipe to be installed with no pitch or even allow the pipe to form a “belly”. A “belly” is where the pipe has fallen and is now moving back up. This is known as being “back pitched”.
3. Long runs of pipe are not considered by the user. For example, when a garbage disposer is in use, the person using the disposer will not allow water to run long enough. What happens is the water continues to run out of the drain, leaving the debris behind.
The video illustrates a few things that are worth investing in when the installation is done. Clean outs, long sweep bends or the use of 45 degree bends and an increase in pipe size, the further away from the vent the pipe gets. This allows for debris to accumulate (not desirable, however, will inevitably occur) and not choke off the air needed to allow water to flow.