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House built 2 years ago ... Long story short, my main sewage line clogged up so bad that water/waste started coming out through the vent pipe. Builder comes over and guy from sewer company comes to take out the clog and starts talking about how the soap scum is clogging so badly but he usually sees this after 10+ years in houses. So, matter of factly, I ask him why this would be the case and his first guess is that there's probably no slope in the drain. I'm unable to find my level and he eyeballs it ... says it looks completely level.

Suffice to say, builder had his plumber come over who nonchalantly adjusts a hanger on the left and says it's good to go (i had to ask him to check with the level ... uses my level to read it, he didn't bring his, of course).

So, I need some help interpreting what I'm reading with my electronic level.
By what i've read on calculating slope and reading through the forums ... I am thinking the first mark at 24" should be higher than the reported 1/8th.

Given that if this were raised a minimum 1" at the start, I would expect the 24" mark to be at least 2-3% in grade and each successive reading should be slightly less than the previous. Looking at these measurements, there's even a good chance it's still sloped backwards towards the cleanout trap (to the left).

To check accuracy, using a regular bubble level, it's almost slightly touching the left line at each mark mentioned below. Using an electronic level, the 3 modes I've put it through are listed below (it's listed with a =- 0.2 degree accurracy range).

- 4", 8 ft pipe to where it connects to the cast iron; so, minimum code for slope should be 1/8th per foot

- mark1 is 24" from the left end; 1/8th, 14mm, 1.4%, 0.8 degree
I would expect the 24" mark to be closer to 2-3% in grade
- mark2 is 48" from the left end; 1/4th, 16mm, 1.75%, 0.95 degree
- mark3 is 72" from the left end; 1/4th, 16mm, 1.8%, 1 degree

I also slid a small level into the cleanout on the end as much as it could go (about half way), the bubble is completely in the middle on that one (the smaller level, the bubble on the 3 marks is right on the left most line).

Is this sloped correctly for even 1/8th per foot? My thinking is that it is not.

* in case anyone nitpicks at the tape in the pic .. this was my first pic .. i made sure each tape mark was at 24, 48 and 72 when i measured ... the middle one was off by 3 inches before I re-did it. i did not take another pic after moving the tape markers*
 

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retired framer
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If your level is 2 ft long, hold it up to the bottom of the pipe and drop one end until it is level, the gap you have dropped it at the end should be 1/4. That would be the same anywhere on that pipe. Smaller pipes, need 1/4" per foot.
 

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