The 10 Most Common Plumbing Mistakes DIYers Make

Updated: Aug. 09, 2023

Get the job done right the first time and save money on expensive repairs down the road.

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Overtightening Connections

Overtightening supply tubes, pipe and fittings and toilet bolts is one of the most frequent mistakes DIYers make. If you crank too hard on a galvanized or black pipe, coupling, tee or elbow, you risk cracking the fitting. The crack may not happen right away, but the excessive force can break the fitting weeks later, causing a flood. Learn how to protect your home with flood vents.

Overtightening the plastic fittings on toilet and faucet supply tubes is even more common. It just doesn’t take that much torque to tighten a water supply line. If you tighten the hex nuts too much, they’ll eventually break and leak. Plus, overtightening toilet closet bolts at the floor or between the bowl and tank can crack the porcelain and destroy the toilet.

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Wrapping Thread Tape Backward or Using the Wrong Tape

PTFE thread tape (commonly called Teflon tape) must wrap clockwise around the threads for it to work properly. But, many DIYers wrap it backward so the tape actually unwinds from the threads as they tighten the fitting. That defeats the whole purpose of using thread tape since it can’t seal if it isn’t embedded in the threads.

Here’s a tip for proper wrapping: Wrap three times around the threads with the last wrap facing to the left as you screw the pipe into the fitting. If that last wrap is pointing to the right, stop and re-wrap it.

Also, use the right tape.

• Use thin white or thick pink thread tape for fittings that carry water.

• Use yellow gas-rated tape for threaded gas line connections.

• Never use thread tape on compression or flare fittings

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clogged sink drains
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Using Drain Cleaners as a First Choice

The easiest way to remove kitchen and bath sink clogs is to use a snake, a barbed drain cleaning tool or even a power auger. Or, simply remove the P-trap and pour out the clog. Too often, people reach for the chemical drain cleaners, pouring in way too much. You’ll want to avoid that because liquid drain cleaner can sometimes create more problems than it solves. Here’s why:

• If the liquid cleaner doesn’t clear the clog, you or your plumber will probably have to remove the trap arm later on and it’ll be filled with caustic corrosive drain cleaner that can be dangerous.

• Using too much drain cleaner, or using it too often, can damage metal traps and pipes, causing leaks.

• Liquid drain cleaner destroys the rubber gasket used in “mission” style couplings. If you have any of those couplings in your drain lines and you use liquid drain cleaners, you’ll damage them, causing leaks in the future.

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Tackling a Plumbing Job Without Spare Parts

DIYers often make the mistake of buying just a cartridge or washer for a faucet repair. But if the washer or cartridge are worn, chances are other faucet parts are worn as well. If you don’t replace the stem seal and gasket, and O-rings when replacing the washer or cartridge, you’ll probably wind up with a leaky faucet.

Those peripheral parts are cheap, so make it a rule to buy them all upfront and “rebuild the faucet” rather than replacing just a single part.

The same rule applies when working on drain lines. If you’ll be disassembling a metal p-trap and arm, make sure you have enough rubber compression gaskets to replace the gasket in every joint you disassemble. The beveled poly washers used on PVC traps and arms can be reused, but you should still have a few spares on hand in case you lose one or discover the old one is cracked.

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Not Turning Off the Water

Many DIYers think they can leave the water on and quickly swap in a new valve. That won’t turn out well.

If you can’t attach the new valve or faucet, you’ll have full water pressure flooding the room and dripping down to the lower floors. Why risk thousands of dollars in damage when all it takes is a few extra minutes to shut off the main water supply valve? Experienced plumbers shut off the water. So should you.

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Using Too Much Muscle On a Stuck Shut Off Valve

Sink and toilet shut off valves tend to seize when not operated for long periods of time. If you can’t turn the knob by hand, don’t think you can solve the problem by applying more muscle. You’ll not only break off the knob, but you can also break off the valve stem at the same time. The problem is that the stem packing seal has welded itself to the valve stem, preventing it from turning.

The fix is use an adjustable wrench to loosen the stem nut just enough to break the bond so you can turn the knob. When you’re done, simply snug up the stem nut and make sure there’s no leak.

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Sweating Copper Pipes With Water in the Line

Pipes and fittings must be completely dry before sweating copper pipes. If there’s any water near where you’re working, it’ll cause the joint to leak. Trust us, we’ve tried heating the water with the torch to boil it off. It doesn’t work. The steam just creates pin-holes in the solder. When you turn on the water, you’ll see fine jets of water shooting out of the joint. Then you’ll have to redo the entire job.

The solution is to plug the pipe with white bread, a special capsule-like plug or a special tool before hitting the joint with a torch.

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Not Having the Right Tools

Plumbers always have the right tools. DIYers often try to skate by and make-do with the tools they have on hand. That’s where things go really wrong. Trying to remove an old galvanized nipple with an ordinary pipe wrench or slip joint pliers can break the pipe and leave the threads in the wall. You can prevent that kind of damage by buying an inexpensive set of internal pipe wrenches. The same advice applies to other plumbing repairs.

• Avoid damaging the finish on your faucet with a strap wrench. Or wrap the jaws of an adjustable wrench with electrician’s tape.

• Remove stubborn faucet supply tubes and fasteners with an extendable basin wrench.

• Get perfectly square cuts on tubing using a tubing cutter rather than a hack saw.

• Speed up copper burnishing with a combination interior/exterior wire brush.

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bad trap connection to vertical drain
Photo: Courtesy of American Society of Home Inspectors

Mixing up Wyes, Tees and Elbows

Knowing which drain fittings to use in each application is critical to avoiding code violations and really unpleasant smells. In this picture, a DIYer has installed a wye to connect the p-trap to the vertical drain. But they had to add a 45-degree elbow to make the horizontal p-trap connection. This setup may look okay, but it’s a code violation that can cause real problems. As it sits, the drain water will flow so fast down the steep slope that it can siphon water out of the p-trap, allowing sewer gas to enter the house.

The DIYer should have used a sanitary tee in this application. Yet, you can’t use a sanitary tee in all drain applications. You can’t use it to connect two horizontal pipes or a vertical pipe to a horizontal drain. Different situations call for a tee, wye or a long or short sweep elbow. Plus, you can’t use 90-degree vent elbow to change direction in a drain line (unless you really like cleaning out clogs). In other words, you’ve got to know when to use each type of fitting.

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Installing a Saddle Valve for an Ice Maker or Humidifier

Piercing saddle valves don’t meet current plumbing codes. Yet, they still come packed in some ice maker and furnace humidifier kits and you can still buy them at home centers. So DIYers continue to install them. That’s a big mistake. Saddle valves are notorious for leaks, especially after being subjected to the shut-and-opened cycle many times. Since they’re often installed in out-of-the-way places, the leak can go unnoticed for months, causing mold problems. Toss the saddle valve and install a ball valve instead. If you’ve already installed a saddle valve, remove it and install a ball-style shutoff valve now before the old valve starts leaking.