How to Slope Drain Lines
How To Slope Drain Lines TIPS
- Drain and vent lines must slope - Period
- Too much slope in a drain line is bad
- WATCH plumbing vent pipe video below
- Support pipes so slope is permanent
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Jennifer Brown, who lives in Panama City, FL, purchased a new home that's got some serious plumbing issues. Read this:
"We purchased a new home about a year ago and have had non-stop plumbing issues. After months of the plumber coming out and telling us there was no problem, it was discovered that one of our pipes was completely level, and since we have a gravity-fed sewer system, the waste was not flowing out to the main line.
After digging up our slab and fixing the slope on one of the pipes, we stopped having sewage back ups but still smelled sewer gas in our laundry room when we used the washing machine. After having the plumber come out once again, he determined that sewage and water were sitting in our pipes.
We are afraid that this is an indication of another pipe that does not have the proper slope. Our builder keeps telling us that it is normal for sewage and water to sit in these pipes since this a gravity-fed system.
Is this correct? The plumber that took video of our line showed us the standing water and waste an indicated that this shouldn't be happening.
I was hoping you could help me because I don't know enough about these types of issues to know if the builder is just trying to save money by not fixing this problem. Any insight would be greatly appreciated."
Master Plumber Tim
I've had a very interesting journey. I'm a college-trained geologist, I became a master plumber before the age of 30 and then did custom building.
Because I'm all of the above, I feel I can speak to Jennifer's issue.
Jennifer, the builder, and his plumber, are IDIOTS and SCAMMERS- and you can quote me on this. I'll also add the Panama City plumbing / building inspectors to the Idiot List too.
Pipes Must Slope
Plumbing AND vent lines are all supposed to be installed with pitch or fall. The generally accepted minimum pitch is 1/8 inch per foot of run.
You can also install pipes with 1/4 inch of fall per foot of run, but I'd be careful about exceeding that slope.
Vent Line Slope
Many homeowners are unaware of the network of vent lines that are part of a plumbing system. You almost always have as much pipe in vent lines as you do in drain lines.
While the vent lines are designed to deliver air to the system from the roof vent pipe, water vapor routinely condenses in the pipes.
This condensate must be allowed to drain back to the sewer or septic tank so the vent lines also must have a minimum fall of 1/8-inch per foot.
Vent Piping Video
Watch this video to see the vast network of vent pipes in a house I plumbed in New Hampshire in 2016.
Too Much Creates Clogs
Plumbing drain lines that are pitched too steeply can clog because the liquids outrun the solids in the pipe. A slope of 1/4-inch per foot of run will ensure you never have issues.
Plumbing Rough-In Diagram
This is a drawing I made to show you the drain and vent lines in a full bathroom that was to be added to an existing home.
Tough Love Conversation
If I could be a tiny imp on your shoulder whispering in your ear when you next have these two noobs over at your house I think the conversation might go like this:
"Mr. Builder and Plumber. The last time you were here, you said it's normal for plumbing lines to be level, right?"
"Ms. Brown, that's correct."
"Well, I did some research. I talked with the local plumbing inspector and he gave me a copy of the code book. It states right there that all drain and vent lines MUST have slope to them so there is no standing water.
Furthermore, I talked with the head of the local sewage department here in Panama City. I asked him if it's a good idea to install sewer lines level. He CRACKED UP LAUGHING saying the sewer lines would rapidly clog up. What say you?"
(Shuffling of feet, throat-clearing noises, eyes pointed to ground) "Well, that's just someone's else's opinion."
"So how about Mother Nature? In the REAL WORLD all drain lines (brooks, streams, creeks and rivers) have SLOPE. Basins that have no slope like ponds, lakes and lagoons eventually FILL UP WITH sediment because there is no slope or fall to them. I want you to fix EVERY drain line in my house that doesn't have the proper fall to it."
Game, set and match.