Ask the Builder: Installing plumbing drain pipes

I’ve always loved doing plumbing because it’s a very interesting three-dimensional challenge to install drain, sewer and vent lines in a new home or a large remodel. Since I was also the chief carpenter and builder at my jobs, I was able to think ahead that all of the frame and raw wood would be installed so that it didn’t have to be butchered to get into the pipes.

Amanda, who lives in South Carolina, contacted me last month. She wanted to know how she could get money from the original plumber who installed the drain pipes in her house. Amanda received bad advice from another plumber or remover who told her that a toilet drain pipe was incorrectly installed by the original plumber.

Amanda paid the new plumber to cut out the perfectly fine pipes and install new ones with smoother bends. Too bad she wasted so much money! She could have spent less than $ 50 and set up a simple phone call to see if she could get any good advice. But that’s water over the dam.

Here was Amanda’s situation. The toilet drain pipe ran about 5 feet between two floor joists. It was then turned over with a normal 90-degree fitting – some call it a short L – and immediately connected to a 90-degree sweep 90-degree fitting so that the toilet waste could continue its way to the sewage treatment plant below the floor joists but now perpendicular to the beams.

She was told the short 90 was inappropriate. I asked her if she had ever had a constipation in the eight years since the house was built. Your answer was no. That’s why she was never constipated. The short 90 degree fitting is similar to the exact change in direction that toilet litter would encounter if the pipe were connected to a standard tee. Plumbers have installed horizontal toilet drain pipes that attach to tees for many decades.

When you flush the toilet, water and sewage run straight down and immediately hit a 90-degree tap under the toilet flange. This 90 degree fitting directs the water horizontally towards the tee fitting, which is perhaps 1 or 2 feet away. When the sewage reaches the middle of the tee, it makes a sharp turn and goes back down. Imagine a river flowing over a waterfall. This is a perfectly acceptable configuration – after all, it has worked well for Mother Nature for millions of years.

Tear out the plaster or drywall and you will discover this exact configuration in millions of homes and buildings across the United States. Plumbers have been using tees since the early 1900s and still use them today. In fact, I used this exact configuration two years ago when I was recording my video about flushable wipes.

In many situations the vertical pipe exiting the bottom of the tee is just a vertical stack. This pipe can be 8 or 9 feet tall. Think of a pipe shaft like a chimney. Sewage goes down the chimney while smoke rises up a chimney.

At the bottom of the piles, it is best to install a Sweep-90 fitting. These fittings have a slightly larger radius than a short 90 fitting. The longer radius is very friendly to sewer cleaning coils. It is precisely for this reason that plumbers have been using Sweep 90 fittings for decades.

In Amanda’s situation, she had an acceptable line structure. It’s just that their stack was only 3 inches tall. There is nothing wrong with that. I’ve done this before where I had to tuck a horizontal drain pipe against floor joists in a basement or crawl space. I’ve never had any issues with constipation.

It is possible that Amanda misunderstood the advice or the plumber who gave the advice was not clear. Any change of direction fittings buried under a plate should never have 90 degree fittings. If you need to change direction in concrete or other buried piping conditions, such as in a sewer line, use two 45 degree fittings. It is a best practice to separate the 45 degree connectors by at least 6 inches if possible. This is an aid to snake drain cleaning.

You can have a 90 degree faucet under a plate, but it either has to be at the base of a stack, as I described earlier, or it can be under a toilet that stands on a plate. If clogging occurs in these two places, it is usually resolved by installing a cleaning tee directly above the bottom of the stack or removing the toilet to check the 90 degree tap.

If you want to learn more about plumbing drainage lines or the mystical plumbing vent lines, I have several videos for you on my website Simply enter “sanitary videos” in the search engine. If you have any questions about your drainpipes, find the Ask Tim navigation link and type your question for me. I would love to help you save time and money.

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