Normal Conditions
Under normal conditions, sewers are installed with a fall of 1/4" per every one foot of length. Under difficult circumstances (and with the city inspector's OK) a bare minimum of 1/8" fall per foot is acceptable, although not preferred
Low Areas
A "low area" (a.k.a. Sag or Belly) is where the sewer pipe has lost positive slope going to its destination, i.e. the city sewer main or in some cases a septic tank. With rare exception, sewers flow by gravity to where it ties onto the city's main sewer and becomes their responsibility. If a line is properly installed, it will have a positive slope for the entire duration of its distance.
off-set pipe joints is the beginning sewage leakage
Roots infiltration catching on waste causing sewage backup, settlement, rats and roots infiltration
Roots, Off-set Pipe Joints, Holes , Settlement, Broken, Rusted Out Pipe are Common In Older waste lines,
1900
When connected sections do not line up perfectly with one another, they are referred to as being "off-set."
Sewer lines built from the 1800's up to the mid 1980's were constructed using a large number of short sections, typically 2' to 4' in length, of VCT (vitreous clay tile) pipe. These sewer lines are particularly subject to off-sets due to their large number of joints. During construction, the joints were sealed with products such as concrete, coal tar, oakum, rubber gaskets, and on occasion, nothing at all. Over time, these sealants erode away, allowing the pipe to then settle down into the "hub" of a connected pipe creating a slight offset. In most clay pipe, off-sets will not exceed 1/4" unless the pipe is broken at the hub. However, this only applied to pipes running in a straight line.
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