A P-trap is actually a U-shaped bend in the drainpipe beneath your sink or other plumbing fixture . When water flows through the drain, a small amount stays behind in that curved section. This leftover water forms an airtight seal so sewer gases can’t travel backward into your home. It’s called a P-trap because, when connected to the drain arm in the wall, the full assembly resembles the shape of the letter “P.” Go ahead at take a look under the sink, we'll wait. P-traps are typically made from: PVC (most common in homes today) ABS (in some regions) Chrome-plated metal (common in older or exposed installations) Bonus tip: Older homes sometimes used S-traps, which loop downward in an “S” shape. These are no longer allowed by code because they siphon dry too easily, causing sewer smells. P-traps replaced them as the safer, modern standard. How P-Traps Work The P-trap uses a very simple physics principle: water blocks air. Here’s what happens each time you run the faucet: Water flows through the drain. Some water stays in the bend of the pipe. That water blocks air from moving backward. Wastewater continues down the drain line toward the sewer. A P-trap can stop working if: the water evaporates (common in rarely used fixtures), the trap gets clogged, the trap leaks, or improper venting causes the trap to siphon empty. Where You’ll Find a P-Trap in a Home P-traps aren’t just under bathroom sinks -- they’re everywhere wastewater leaves a fixture. 1. Under Sinks Kitchen sinks Bathroom sinks Laundry/utility sinks These are the most visible and the easiest to service. 2. Showers, Tubs & Floor Drains You won’t see these traps, but they’re there -- hidden under the floor or inside the framing. 3. Appliances & Laundry Drains Washing machines and some dishwashers connect through systems that rely on a plumbing trap to prevent sewer odors. Do Showers Have P-Traps? Yes. Building code requires every shower to have a functioning P-trap. Why it matters: Prevents sewer odors Catches hair/soap debris before it reaches the main line Maintains sanitary indoor air If you smell sewage near a shower, the trap may be: clogged, dry, cracked, or not installed correctly. Do Toilets Have P-Traps? Yes, but not the kind you see under a sink. A toilet has a built-in P-trap molded directly into the porcelain bowl. This is why water always sits in the bottom of the toilet — that’s the trap seal preventing odors. Because toilets have their own internal traps, they do not use an additional trap in the floor line. Common P-Trap Problems & How to Fix Them Even though P-traps are simple and reliable, a few issues come up again and again in Albuquerque homes. The most common include dry traps, leaks, cracks, clogs, and installation mistakes. Knowing the signs early helps you avoid sewer odors, water damage, and costly repairs down the line. 1. Dry P-Traps (Very Common in Guest Bathrooms) A P-trap needs water to seal out sewer gases. When a sink, shower, or floor drain isn’t used regularly, the water in the trap slowly evaporates. Once the water seal disappears, nothing stops those sewer gases from creeping into your home. Signs of a Dry Trap Strong sewer or “rotten egg” smell near the drain Odor returns even after cleaning the sink Gurgling sounds when water runs in nearby fixtures How to Fix or Prevent It Run water for 10–15 seconds at least once a week in unused bathrooms or basements. If the odor returns immediately, the trap may have a leak or venting issue that needs attention. 2. Leaks and Cracks in the P-Trap Leaks are the second most common P-trap issue. They typically occur from: Corrosion (older chrome or metal traps rust over time) Improper installation Loose slip-joint nuts and worn washers Physical shifting or impact inside the cabinet Cracks in older or thin plastic traps Because the trap sits under the sink, leaks often go unnoticed until they’ve caused damage. Warning Signs Water droplets or pooling under the sink Musty smell in the cabinet Swollen, warped, or discolored wood Mold or mildew spots Why It Matters Even small, slow leaks can cause rot, cabinet damage, mold growth, or a broken trap seal — allowing sewer gases into your home. What to Do Tighten slip nuts gently — overtightening can crack the trap. If corrosion, cracks, or brittle plastic is visible, replacement is the safest option. PVC and ABS traps are good modern upgrades because they resist corrosion and damage. 3. Clogged P-Traps Clogs form when debris builds up inside the bend of the trap. For sinks and showers, this often includes: Hair Grease Soap scum Food particles Shaving products Sediment buildup Signs of a Clogged Trap Slow draining Standing water in the sink or shower Gurgling after draining Sewer odors even when the trap has water Why You Should Avoid DIY Chemicals Chemical drain cleaners can: Corrode metal traps Damage older plastic traps Sit in the trap if the clog doesn’t clear, causing further deterioration Release fumes that are hazardous indoors Wire-hanger-style DIY methods can scratch the inside of the pipe, creating rough surfaces where future clogs form even faster. Best Solution Have a licensed plumber safely remove and clear the trap, check the rest of the drain line, and ensure no deeper blockage is forming. 4. When to Replace Your P-Trap Instead of Repairing It A full replacement may be needed if: The trap is heavily corroded Cracks are visible Fittings no longer tighten properly Odors persist even after cleaning The trap was improperly installed You’ve repaired leaks more than once New PVC or ABS traps are durable, affordable, and handle moisture better than old metal ones. Regular Maintenance Helps Prevent Major Problems Routine drain cleaning and periodic plumbing inspections help catch issues early. A plumber can confirm: The trap has a solid seal The drain arm has proper slope Venting is correct No double-trapping exists No hidden leaks or slow drips are starting This type of maintenance protects your home from both sewer odors and long-term water damage, especially in older Albuquerque neighborhoods with aging plumbing. When to Call a B. Carlson Plumber If you’re dealing with sewer smells, slow drains, leaks under the sink, or recurring P-trap issues, the safest move is to call a professional. A licensed plumber can diagnose whether the trap is the problem or if something deeper is happening in your drain or vent system. At B. Carlson Heating, Air Conditioning & Plumbing, our expert plumbers handle everything from clearing clogs to replacing damaged traps to fixing underlying venting or drain issues. We’ve been helping Albuquerque homeowners stay safe and odor-free since 1971 — and we’re available 24/7 when you need us most. If something doesn’t smell right or drain right, call B. Carlson right away.

fixtures, maintain, plumbing, repair

What is a P-Trap?

A P-trap, or plumbing trap, is the curved section of pipe under sinks, showers, tubs, and other drains. It holds a small amount of water that blocks sewer gases from entering your home while still allowing wastewater to drain away. Every modern plumbing fixture (except toilets, which have built-in traps) uses a P-trap to keep indoor air safe and odor-free.

A P-trap is actually a U-shaped bend in the drainpipe beneath your sink or other plumbing fixture. When water flows through the drain, a small amount stays behind in that curved section. This leftover water forms an airtight seal so sewer gases can’t travel backward into your home.

It’s called a P-trap because, when connected to the drain arm in the wall, the full assembly resembles the shape of the letter “P.” Go ahead at take a look under the sink, we’ll wait.

P-traps are typically made from:

PVC (most common in homes today)
ABS (in some regions)
Chrome-plated metal (common in older or exposed installations)

Bonus tip: Older homes sometimes used S-traps, which loop downward in an “S” shape. These are no longer allowed by code because they siphon dry too easily, causing sewer smells. P-traps replaced them as the safer, modern standard.

How P-Traps Work

The P-trap uses a very simple physics principle: water blocks air.

Here’s what happens each time you run the faucet:

Water flows through the drain.
Some water stays in the bend of the pipe.
That water blocks air from moving backward.
Wastewater continues down the drain line toward the sewer.

A P-trap can stop working if:

the water evaporates (common in rarely used fixtures),
the trap gets clogged,
the trap leaks,
or improper venting causes the trap to siphon empty.

Where You’ll Find a P-Trap in a Home

P-traps aren’t just under bathroom sinks — they’re everywhere wastewater leaves a fixture.

1. Under Sinks

Kitchen sinks
Bathroom sinks
Laundry/utility sinks

These are the most visible and the easiest to service.

2. Showers, Tubs & Floor Drains

You won’t see these traps, but they’re there — hidden under the floor or inside the framing.

3. Appliances & Laundry Drains

Washing machines and some dishwashers connect through systems that rely on a plumbing trap to prevent sewer odors.

Do Showers Have P-Traps?

Yes. Building code requires every shower to have a functioning P-trap.

Why it matters:

Prevents sewer odors
Catches hair/soap debris before it reaches the main line
Maintains sanitary indoor air

If you smell sewage near a shower, the trap may be:

clogged,
dry,
cracked,
or not installed correctly.

Do Toilets Have P-Traps?

Yes, but not the kind you see under a sink.

A toilet has a built-in P-trap molded directly into the porcelain bowl. This is why water always sits in the bottom of the toilet — that’s the trap seal preventing odors.

Because toilets have their own internal traps, they do not use an additional trap in the floor line.

Common P-Trap Problems & How to Fix Them

Even though P-traps are simple and reliable, a few issues come up again and again in Albuquerque homes. The most common include dry traps, leaks, cracks, clogs, and installation mistakes. Knowing the signs early helps you avoid sewer odors, water damage, and costly repairs down the line.

1. Dry P-Traps (Very Common in Guest Bathrooms)

A P-trap needs water to seal out sewer gases. When a sink, shower, or floor drain isn’t used regularly, the water in the trap slowly evaporates. Once the water seal disappears, nothing stops those sewer gases from creeping into your home.

Signs of a Dry Trap

Strong sewer or “rotten egg” smell near the drain
Odor returns even after cleaning the sink
Gurgling sounds when water runs in nearby fixtures

How to Fix or Prevent It

Run water for 10–15 seconds at least once a week in unused bathrooms or basements.
If the odor returns immediately, the trap may have a leak or venting issue that needs attention.

2. Leaks and Cracks in the P-Trap

Leaks are the second most common P-trap issue. They typically occur from:

Corrosion (older chrome or metal traps rust over time)
Improper installation
Loose slip-joint nuts and worn washers
Physical shifting or impact inside the cabinet
Cracks in older or thin plastic traps

Because the trap sits under the sink, leaks often go unnoticed until they’ve caused damage.

Warning Signs

Water droplets or pooling under the sink
Musty smell in the cabinet
Swollen, warped, or discolored wood
Mold or mildew spots

Why It Matters

Even small, slow leaks can cause rot, cabinet damage, mold growth, or a broken trap seal — allowing sewer gases into your home.

What to Do

Tighten slip nuts gently — overtightening can crack the trap.
If corrosion, cracks, or brittle plastic is visible, replacement is the safest option.
PVC and ABS traps are good modern upgrades because they resist corrosion and damage.

3. Clogged P-Traps

Clogs form when debris builds up inside the bend of the trap. For sinks and showers, this often includes:

Hair
Grease
Soap scum
Food particles
Shaving products
Sediment buildup

Signs of a Clogged Trap

Slow draining
Standing water in the sink or shower
Gurgling after draining
Sewer odors even when the trap has water

Why You Should Avoid DIY Chemicals

Chemical drain cleaners can:
Corrode metal traps
Damage older plastic traps
Sit in the trap if the clog doesn’t clear, causing further deterioration
Release fumes that are hazardous indoors

Wire-hanger-style DIY methods can scratch the inside of the pipe, creating rough surfaces where future clogs form even faster.

Best Solution

Have a licensed plumber safely remove and clear the trap, check the rest of the drain line, and ensure no deeper blockage is forming.

4. When to Replace Your P-Trap Instead of Repairing It

A full replacement may be needed if:

The trap is heavily corroded
Cracks are visible
Fittings no longer tighten properly
Odors persist even after cleaning
The trap was improperly installed
You’ve repaired leaks more than once

New PVC or ABS traps are durable, affordable, and handle moisture better than old metal ones.

Regular Maintenance Helps Prevent Major Problems

Routine drain cleaning and periodic plumbing inspections help catch issues early. A plumber can confirm:

The trap has a solid seal
The drain arm has proper slope
Venting is correct
No double-trapping exists
No hidden leaks or slow drips are starting

This type of maintenance protects your home from both sewer odors and long-term water damage, especially in older Albuquerque neighborhoods with aging plumbing.

When to Call a B. Carlson Plumber

If you’re dealing with sewer smells, slow drains, leaks under the sink, or recurring P-trap issues, the safest move is to call a professional. A licensed plumber can diagnose whether the trap is the problem or if something deeper is happening in your drain or vent system.

At B. Carlson Heating, Air Conditioning & Plumbing, our expert plumbers handle everything from clearing clogs to replacing damaged traps to fixing underlying venting or drain issues. We’ve been helping Albuquerque homeowners stay safe and odor-free since 1971 — and we’re available 24/7 when you need us most.

If something doesn’t smell right or drain right, call B. Carlson right away.