Plumbing Tips: ABS Pipe

Les talks plastic pipes

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

Tip 1: Les is an ABS Guy

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Les with ABS plastic pipe

Les and his plumbing buddies all use ABS pipe for drain lines and plumbing vents.

“I pretty much only use ABS black pipe and rarely use the white PVC stuff. It’s all about the glue. Gluing ABS is a one-step process, which makes it faster to work with than PVC. Purple PVC primer is messy, emits noxious fumes, and it’s just ugly.”

ABS cement lasts longer in the can and dries clear, making it more forgiving if you get a drip or two on the floor. ABS cement also dries faster, which reduces the risk of connections pushing apart before they set up. Les believes the labor saved by using ABS more than makes up for the extra money spent on pipe and fittings. ABS is also lighter and more flexible. He says that makes it easier to flex for bending it into tight spaces.

“It’s not only me. None of my plumber buddies use PVC either.” The only downside—retailers don’t always carry ABS.

Tip 2: Use dull blades for bigger or tighter cuts

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Cutting ABS with a dull wood blade

Dull wood blades cut ABS cleanly without chatter or melting the plastic.

When Les cuts larger pipe or has trouble getting the tubing cutter (see Tip 11) into tight spaces, he uses a reciprocating saw fitted with an older, dull wood blade. “A new wood blade with aggressive teeth tends to grab on to the pipe and rattle the whole works, and a metal blade melts the plastic rather than cuts it.”

Tip 3: You can reuse a landlocked fitting

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Socket Saver tool

This special tool allows you to ream out old, glued-on pipe from a fitting and save the fitting for reuse.

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.” Find Socket Savers for $18 to $35 through our affiliation with amazon.com.

Tip 4: Don’t glue yourself into a corner

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Pipe assembly

Plan pipe assembly so you glue in the moveable pipes last.

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 because one or both of the pipes don’t move enough to slide the fitting on.

“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.

Tip 5: Deburr for leak-free connections

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Deburring a plastic pipe

Scrape off burrs left from the saw with a utility knife.

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’ll get leaks or flunk a pressure test. Les always scrapes away burrs with a utility knife before joining the pipes.

Tip 6: Avoid call-backs: Use straps

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Plastic strap supports

Use plastic straps rather the plastic J-hooks to support horizontal runs.

Changes in temperature can cause changes in the length of plastic pipes. When you hang pipe from plastic J-hooks, you’ll 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.

Tip 7: Learn Les’ elbow rule

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Elbow options

Pick the appropriate elbow depending upon pipe content (air or water) and water flow direction (horizontal or vertical).

For pipes under 3 in., 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.”

Tip 8: Skip those closet flange slots

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Toilet mounting flange

Mount the toilet flange with the notches parallel to the wall and avoid using the slots for the closet bolts.

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 makes sure the notches are parallel to the wall behind the toilet. “One more thing: Don’t use flanges with metal collars—metal rusts.”

Tip 9: Support hot drain lines

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Support for hot drain lines

A 2-in. pipe supports the 1-1/2-in. drain line.

Drain lines that routinely drain extremely hot water need continuous support. “Lines under sinks that are connected to dishwashers are the most common culprit.” Those pipes will sag between ordinary supports.

Here’s another Les trick: “Slide a larger pipe over the drain line before attaching any fittings, and then attach the supports to that.”

Tip 10: Seal the ends!

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Seal end cuts

Seal pipe ends with ABS cement.

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.” 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’ll fail a pressure test every time. “Can you even imagine that disaster? You’d have to replumb everything!”

Tip 11: Les loves tubing cutters

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Tubing cutter

This large-size tubing cutter cuts plastic pipe up to 2-in. in diameter.

For pipes up to 2-in., Les prefers a tubing cutter (a giant version of the type used for copper tubing). “It makes a perfectly straight cut with no burrs or shavings to clean up. But best of all, it doesn’t take up much room in the tool bucket.” You can get them for about $25 at home centers.