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Gravel clogged sewage pipe/lateral: how and what to do about it.
In an earlier thread, https://www.askmehelpdesk.com/plumbi...or-184273.html , I described three stages of digging in the basement (perimeter French drain; replacement of sewage pipes; then smaller section of French drain). The smaller French drain, put in the end of February, was needed to catch water entering the ‘end’ of the basement, where the sewage pipes connect to the lateral pipe (90' long) that goes out through the back yard to the city’s 10" sewage pipe. Early March, after a hard rain, I noticed sewage water and toilet paper had backed up through a drain at the end of the basement. Clearly, the lateral was clogged. I paid a plumber to come in and use a drain borescope to look down the lateral. He found a major blockage by gravel half way down the lateral. He was able to break the blockage with his auger, but the gravel – about a bucket full – is lying along a five to 10 foot stretches of pipe, again, about 45 to 50' along the lateral. [I have a video of the lateral with the gravel, and a video taken two years earlier, showing a ‘clean’ lateral.] He told me, however, that I must ‘pressure hose’ out all the gravel in the lateral, or I would have another blockage soon. He estimated that it would cost around $2000 or more to do the job. But my first question is: where did the gravel come from?
It’s possible that during the replacement of sewage pipes, back in October, the plumbing crew accidentally got lots of gravel in the pipe while they were digging out the subsurface caste iron pipe, circa 1950, and replacing it with PVC pipe. They tied the PVC pipe into the caste iron about 3' from the end of the basement. Alternatively, the French drain crew could have cracked into drain pipes in several areas, and the gravel could have spilled into the pipe. One place is an old washbasin drain (2") pipe, which passes the drain at the end of the basement on the way to the lateral. Another is the main caste iron pipe going to the lateral; the trench ran perpendicular to the pipe at the end of the basement.
During the latest heavy rain, I was able to see the flow of water from the French drain passing along the former washbasin drain pipe. I sampled some of the water, and it contained lots of brown dirt, indicating that the drain pipe was indeed connected to the French drain - an obvious mistake on the part of the French drain crew. However, I cannot believe that so much gravel (see attached photos) could have traveled the 12' along a 2" drain and made its way 45' down the lateral. Instead, my intuition tells me that the French drain crew must have breached the 4" caste iron pipe at the end of the basement, and the gravel entered the lateral from there, after the crew backfilled the trench with gravel.
These are my speculations. I’d appreciate hearing any thoughts on how the gravel could have gotten into the laterals. And, even more, I’d like to hear some solutions to cleaning out the gravel, especially solutions that won’t cost $2000. For added information, I know the location where my 4" lateral enters the city’s 10" sewage line. There’s a manhole on my property, and the lateral ties in about 1' from the bottom of the manhole. So I might be able to get to the gravel from the city’s sewage line end.
Thanks, again, to all of you for your considerations. ILS^2
