Tips for Plumbing With Plastic Pipe

We asked Les Zell, our resident master plumber, to share some of his tips on working with plastic plumbing. Here are a few of his best.

A stack of plastic pipesFamily Handyman

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Plastic pipe plumbing tips from an expert

We asked Les Zell, a master plumber, to tell us some of his tips on working with plastic plumbing pipes. Not surprisingly, with 25 years in the industry, he had plenty to share. Here are a few of his best tips and advice.

slicing through plastic pipe with a dull blade
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Use dull blades in a pinch

When Les cuts larger pipe or has trouble getting the tubing cutter into tight spaces, he uses a reciprocating saw. If he can't find his PVC blade he reaches for an older, dull wood blade. A new wood blade with aggressive teeth tends to grab on to the pipe and rattle the whole works, while a metal blade melts the plastic rather than cut it.

connecting plastic pipes with pipe glue
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Don't glue yourself into a corner

In many assemblies, there are pipes that move and pipes that don’t. If you start gluing fittings together willy-nilly, you may end up in a situation where you’re unable to attach the last fitting “The last fitting to be glued should be the one on a pipe that has a little wiggle room.” That’s usually where a vertical run meets a horizontal one so you can snug on an elbow or a tee from two directions.

a socket saver inside pipe cutter
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You can reuse a landlocked fitting

If you have to replace some piping but it’s tough to replace the fitting, it’s possible to ream out the old fitting and reuse it. This happens a lot. Let’s say there’s a tee coming out of the back of a cabinet with a broken pipe leading to it. Or the fitting is so buried up in the floor joists that you can’t get at it. Les just cuts off the pipe near the knuckle, then uses a Socket Saver to ream out the pipe to expose the inside of the fitting. Then he can cement a new pipe into the old fitting and reuse it. “It’s a lot simpler than ripping out cabinets or drywall or concrete to replace the fitting.”

Deburring a pipe for better connections
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Deburr for leak-free connections

Leftover burrs on the end of a pipe will create channels in the cement when you push the fitting onto the pipe—and then stay there like little canals. That’s when you will get leaks or flunk a pressure test. Les always scrapes away burrs with a utility knife before joining the pipes.

strapping pipes to walls to avoid callbacks
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Avoid callbacks—use straps

Changes in temperature can cause changes in the length of plastic pipes. When you hang pipe from plastic J-hooks, you will hear a tick when the pipe slips past the J-hook. Les says he gets tons of service calls from panicky customers believing these ticks to be water drips from a leaky pipe, “But they can never find the leak!” He generally uses plastic straps and never gets false alarm calls on his plumbing.

plastic pipe elbows
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Learn the elbow rule

For pipes under 3 inches, there are three basic types of 90-degree elbows: vent, short sweep and long sweep. Vent elbows are easily identified by their drastic bend and can only be used on a vent run that carries air, not water.

Les has a good system to remember when to use the other two types of elbows: “If water is speeding up as it turns the corner (usually going from horizontal to vertical), use a short sweep. If water is slowing down (usually from vertical to horizontal), use a long sweep.”

a closet flange
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Skip those closet flange slots

Les has serviced dozens of toilets with broken closet flanges. Toilets are top-heavy, which stresses the closet bolts that hold a toilet to the closet flange. The plastic on the sides of the adjustable slots that receive the bolts is thin and prone to cracking. Les always turns the flange 90 degrees and anchors the toilet using the notches instead. He also makes sure the notches are parallel to the wall behind the toilet.

“One more thing," said Les. "Don’t use flanges with metal collars—metal rusts.”

give support to hot drain lines
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Support hot drain lines

Drain lines that routinely drain extremely hot water need continuous support. “Lines under sinks that are connected to dishwashers are the most common culprit,” said Les. Those pipes will sag between ordinary supports. Here is Les' tip for this scenario: Slide a larger pipe over the drain line before attaching any fittings, and then attach the supports to that.

Sealing the ends of a plastic pipe
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Seal the ends!

Most ABS pipes have either a cellular or a foam core that air will actually pass right through. “If you don’t believe it, wrap your lips around the pipe wall and blow through it,” said Les. If you don’t seal pipe ends with cement, air will escape into the porous center core and find its way out of the plumbing system and you will fail a pressure test every time.

“Can you even imagine that disaster?" Les added. "You’d have to re-plumb everything!”

cutting through a plastic pipe with tubing cutters
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Les loves tubing cutters

For pipes up to 2 inches, Les prefers a tubing cutter (a bigger version of the type used for copper tubing).

“It makes a perfectly straight cut with no burrs or shavings to clean up," said Les. "But best of all, it doesn’t take up much room in the tool bucket.”

Les Zell, a plumber
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Meet the Expert

Les Zell has been a master plumber for thirty years and is owner and operator of Zell Plumbing and Heating, St. Paul, MN