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How to avoid DIY plumbing mistakes

Here’s a homeowner’s attempt at installing a DIY toilet. He’s already made two grave mistakes. (Tim Carter)

I’m blessed. Not only do I get emails each day from readers like you, but I also get questions from the Ask Tim page at my website. Believe it or not, these questions are never tiring, and it’s like Christmas morning when I open them. The high-resolution photos that often accompany the inquiries are like eye candy to me. My wife thinks I’m nuts!

Wayne reached out to me from Houston. He decided that he was going to do some serious DIY plumbing at his house, and as he put it, “I’ve racked my brain and can’t come up with a code-approved way to make this happen.”

It just so happens that I’m a master plumber. I’ve been one since age 29. I did all the plumbing on most of my jobs and thoroughly enjoyed it. Designing and installing plumbing drain and vent lines is like a giant 3-D puzzle to me. As crazy as it sounds, it’s fun.

I’m not going to try to transform you into a plumber with this column, but I’d like to share some pointers that might come in handy if you decide you want to do what Wayne’s trying to accomplish. If you want to leave the job to real plumbers, the tips might allow you to verify that they’re using the best practices at your home.

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Transporting wastewater from your home to a city sewer or your own septic tank is serious business. In the late 1800s, when indoor plumbing started to take hold, plumbers were as esteemed as the physicians of the time. Once it was understood that sewage was the cause of serious disease, anyone who was willing to pipe it away safely was considered to have a superpower of sorts.

The drain and vent pipes in your home mimic what Mother Nature does on a much grander scale. The problem is that most people don’t stop to ponder what they see with their eyes.

Look at how creeks, streams and rivers work. Small streams eventually connect with larger rivers. When they intersect, the angle is rarely a hard 90-degree turn but more often some gentle angle close to 45, 30 or 22 degrees.

The blood vessels in your body are designed the same way. Don’t ignore technology that Mother Nature has perfected when it comes to the best way for liquids to flow.

You should design your wastewater pipes in a similar manner, for the most part. It’s a bad plumbing practice to have a hard 90-degree bend in a horizontal drain line that’s buried in a slab or otherwise hidden. If you have to make a 90-degree bend, use two 45-degree fittings and put a small piece of straight pipe between the fittings, if possible.

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It’s fine to have a larger-radius (sweep) 90-degree bend at the base of a vertical drainage stack where the wastewater starts to travel horizontally. It’s also a good idea to have a sweep 90-degree fitting where a drain pipe pops out of a wall for a kitchen, vanity or laundry sink.

Don’t forget about pipe slope. Use gravity’s magic force to get solid and liquid waste out of your home. All drain lines should have a minimum fall of an eighth of an inch per foot of horizontal run. Some codes allow a quarter-inch of fall per foot.

If you slope the pipe much more than a quarter-inch per foot, you can set yourself up for future clogs, as the liquids may outrun the solids in steep-pitched pipes. The solid waste may sit in the pipe and accumulate, creating a clog. Avoid the temptation to create lots of fall in your horizontal drain piping.

If you’re unclear about the magic vent lines in your home, you should watch a video I taped. Just visit and type “how to vent plumbing video” into my search engine. This video will get you up to speed so you don’t make critical venting mistakes!

Need an answer? All of Tim’s past columns are archived free at You can also watch hundreds of videos, download Quick Start Guides and more.