Plumbing in the Home/Pipe Belly Under Home


I would like to get feedback on the following plumbing issue I am having:
1) My home (15 years old) has a 25 ft. belly under the foundation.  The 4" PVC pipe is about 85% full of water for 10-15 feet of the belly...tapers out on each end.  
2) Have had 2 stoppages in the last 6 months
3) Until the second stoppage, no care was taken with respect to what was being put down the kitchen sink
4) We are now using a strainer so no solid food goes down the drain

Several plumbers have come out and all want to repair the belly by digging under the foundation (28ft of digging).  Another idea is to re-route that line away from the home and dig a trench throug the front yard to the main sewer line.  QUESTION: If I don't fix the belly, what are the chances that the water would cause the PVC pipe to break and leak water under the house and cause foundation issues?

Hi George,
Having a "belly" on the main line is never a good thing. The code/standard is a minimum of 1/8th inch per foot continuous fall (slope) for 4" pipe.  You have a reverse fall in part of the drain line.  Is this pipe below grade (buried)?  If so, the only way to correct this is to dig it up and regrade it. Seems like it was poorly installed in the first place.  If not, it might be able to be supported from below or properly hung with straps as it should be to correct the fall. Obviously it will be more prone to clogging in it's current condition.  

PVC is pretty strong and it is unlikely that it would ever actually break but anything is possible given the right conditions. Also, if you are in an area that is subject to freezing, the waste water can freeze and block the pipe.  This is very difficult to deal with.  Been there, done that in the high Sierras. LOL  With proper fall and drainage, the water is never standing in the pipe and there is nothing to freeze.  

Re-routing might be an option.  Less under-house digging that way.  Digging under the house can have unwanted consequences like undermined pier footings etc. I frequently find compromised footings caused by plumbers digging with no thought for the damage they are doing to other systems.  A small plumbing repair or main line repair can cause thousands of dollars of foundation damage which, in turn, can cause structural problems. This is NOT something that should be done by amateurs or unlicensed and UNINSURED "plumbing" contractors.
Good Luck,

Plumbing in the Home

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Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


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