I’ve been a master plumber since 1981. I’ve always loved plumbing because it’s a three-dimensional challenge to install drain, waste and vent (DWV) piping in a new home or on a large remodeling job. Because I was the lead carpenter and builder on my jobs, I could think ahead to ensure that all the framing and rough lumber were installed so they wouldn’t get damaged during pipe installation.

Two weeks ago a reader in South Carolina reached out to me. She wanted to know how she could get a refund from the original plumber who placed drainpipes in her home. She believed she had received bad advice from the original plumber based on a conversation with another plumber who told her a toilet drainpipe was incorrectly installed at the outset.

This homeowner paid the new plumber to cut out the perfectly fine pipes and install new ones with more gentle bends in them. What a shame she wasted so much money!

Here was her situation: The toilet drainpipe ran in between two floor joists for about 5 feet. It then turned down using a normal 90-degree fitting — some call it a short bend L — and immediately connected to a sweep 90-degree fitting that was rotated 90 degrees so waste could continue its journey by running under the floor joists but now perpendicular to them.

She was told the 90-degree fitting was a problem. I asked her if she had ever experienced a toilet clog in the eight years since the house was built. Her answer was no.

Here’s why she never had a clog: The short 90-degree fitting resembles the exact change of direction toilet waste would encounter if the pipe was connected to a standard tee fitting. Plumbers for many decades have installed horizontal toilet drain pipes that connect to tee fittings.

When you flush the toilet, water and waste head straight down and immediately hit a 90-degree fitting under the toilet flange. This 90-degree fitting sends the water horizontally toward the tee fitting typically a foot or two away. When wastewater reaches the center of the tee, it takes a sharp turn and heads down again. Think of a river going over a waterfall. This is a completely acceptable configuration — it’s worked well for Mother Nature for millions of years.

Tear out plaster or drywall and you’ll discover this exact configuration in millions of houses and buildings all across the U.S. Plumbers have used tee fittings since the early 1900s, and they still use them today.

In many situations, the vertical pipe that leaves the bottom of the tee fitting is just a vertical stack. This pipe might be 8 or 9 feet tall. Think of a plumbing stack as a chimney. Waste water goes down the stack, just as smoke goes up a chimney.

At the bottom of stacks, the best practice is to install a sweep 90-degree fitting. These fittings have a slightly greater radius than a short fitting. The longer radius is very friendly to drain-cleaning snakes. This is exactly why plumbers have used sweep fittings for decades.

In Amanda’s situation, she had an acceptable piping setup, but her stack was only 3 inches tall. There’s nothing wrong with that. I’ve run into situations where I’ve had to install a horizontal drain pipe against floor joists in a basement or crawl space. I’ve never had clog issues.

It’s possible that she misunderstood the advice she was given or the plumber giving the advice wasn’t clear. Change-of-direction fittings buried under a slab should never have 90-degree fittings. If you need to change direction under concrete or other buried piping conditions such as a sewer line, you use two 45-degree fittings. It’s a best practice to separate the 45-degree fittings by at least 6 inches, if possible. This aids the efficacy of drain cleaning snakes.

You can have a 90-degree fitting under a slab, but it needs to be either at the base of a stack, as I’ve already described, or it can occupy space under a toilet that sits on a slab. If there’s a clog at these two locations, it’s usually remedied by installing a clean-out tee just above the base of the stack or by removing the toilet to inspect the 90-degree fitting.

If you want to know more about plumbing drain lines or mystical plumbing vent lines, I’ve got several videos for you on my website, AsktheBuilder.com. Just type “plumbing videos” into the search engine once there. If you have questions about your plumbing drainpipes, look for the Ask Tim navigation link and type your question to me. I’d love to help you save time and money.

Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.