We just completed a new home about 8 months ago and the plumber did not cap off the last sink waste drain for the rough in plumbing. We had 2 occurances of clogging within 4 months in the pipes under the slab before the pipe was discovered and none since. The uncapped pipe was detected because waste came pouring out of it when they were power snaking the drain.

Nothing was flushed or put in the drains but normal waste. We are on a septic system and the usual precautions are in place such as no paper except toilet paper, minimal use of garbage disposal etc.

My question is could the pipe not being capped be the cause of the clogs if not any suggestions?

Thanks
******Update******
As a Thanksgiving present the master shower and toilet has backed up again. This is where it has happened each and every time. Each time the back up begins when the washer is draining. The house is under "warranty" but the plumber thinks we are doing something to make it clog but nothing could be further from the truth. We had a huge rainstorm over the past 24 hours but the septic company says the aerobic system is working properly.



Edited 1 times.

you need to have a camera inspection of the underground drainage system.
it sounds like something is not sloped correctly.

My friend had a similar problem with a new home. The second floor utility room drains would overflow when the washing machine was in use.

The builder swore up and down it must have been her or her kid's fault.

We finally had a camera inspect and found a big "belly" sag in the drain line. I guess enough water would sit there so it would cause enough resistance to the washing machine water under pump pressure.