Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

Clearing a Blocked Drain

Sink, basin, bath and shower — plunger, trap and hand drain auger
ApplicabilityHousehold sink, basin, bath and shower drains with an accessible trap
Task time34 min editorial estimate, not a measurement
PersonnelOne
Revisionv1 · 2026-07-29
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

A drain that empties slowly, or not at all, is almost always blocked close to the fixture. Hair, soap and grease build up in the trap under the sink, or in the short length of pipe behind it, over months rather than overnight. A cup plunger shifts most of them, cleaning the trap by hand shifts most of the rest, and a hand drain auger reaches what is left. This page covers a sink, a basin, a bath and a shower, and it uses two hand tools and no chemicals.

It also says where to stop. If every drain in the building is slow at the same time, the blockage is not under your sink and nothing here will reach it. That is a plumber's job, and the page says so rather than sending you further down a pipe you cannot see. We do not print a chemical drain cleaner dose or a temperature limit for your pipe, because neither can be traced to a source that applies to your plumbing.

Safety

WARNING

DO NOT DO THIS PROCEDURE IF A CHEMICAL DRAIN CLEANER IS IN THE FIXTURE.
The chemical can splash and burn your skin and your eyes.

Necessary equipment

ItemNote
Cup plungerThe cup must be larger than the drain opening.
Hand drain augerUse a hand drain auger for a fixture drain.
Rubber glovesThe gloves must cover your wrists.
Eye protectionUse safety glasses or goggles.
BucketThe bucket must go below the trap.
Stiff brushThe brush must go into the trap.
Old towelsThe towels keep the water off the floor.
Adjustable wrench optionalUse the wrench only if the nuts do not move by hand.
Flashlight optionalSome drain openings are in a dark space.
Hot water materialWater from the hot tap is enough.
Refuse bag materialPut the waste from the trap into the bag.

Specifications

Chemical drain cleaner compatibility with your pipe
Unverified — do not rely on this value
CONSULT THE PIPE MANUFACTURER AND THE PRODUCT LABEL

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Maximum water temperature limit for your waste pipe
Unverified — do not rely on this value
CONSULT THE PIPE MANUFACTURER

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Find the blockage

Estimated 4 min

NOTEThe trap holds water to stop the smell of the drain. Most blockages are in the trap, or in the pipe after the trap.
  1. Run water into each drain in the building.
    2m
  2. If only one drain is slow, continue with this procedure.
    <1m
  3. If all the drains are slow, stop this procedure. Speak to a plumber.
    <1m
  4. Look into the drain opening with a flashlight.
    <1m
  5. Remove the hair and the soap from the drain opening.
    <1m

Prepare the area

Estimated 1 min

WARNING

PUT ON THE GLOVES AND THE EYE PROTECTION BEFORE YOU TOUCH THE DRAIN.
Waste water has bacteria in it.

  1. Put on the rubber gloves.
    <1m
  2. Put on the eye protection.
    <1m
  3. Put the old towels on the floor.
    <1m

Use the plunger

Estimated 5 min

  1. Put a wet cloth into the overflow opening of the fixture.
    • A sink and a basin have the overflow opening below the rim.
    • A bath has the overflow opening below the tap.
    <1m
  2. Remove the stopper from the drain.
    <1m
  3. Fill the fixture with enough water to cover the cup of the plunger.
    <1m
  4. Put the cup of the plunger over the drain opening.
    <1m
  5. Make a seal between the cup and the surface of the fixture.
    <1m
NOTICE

DO NOT USE MORE FORCE THAN NECESSARY WITH THE PLUNGER.
Too much force can cause damage to an old waste pipe.

  1. Move the plunger up and down quickly for 20 seconds.
    <1m
  2. Remove the plunger from the drain opening.
    <1m
  3. If the water drains away, the blockage is clear.
    <1m
  4. If the water stays in the fixture, do the plunger procedure two more times.
    2m
  5. If the fixture does not drain, continue with the next section.
    <1m

Clean the trap

Estimated 9 min

  1. Close the water supply valve below the fixture.
    <1m
  2. Put the bucket below the trap.
    <1m
WARNING

DO NOT REMOVE THE TRAP IF A CHEMICAL DRAIN CLEANER IS IN THE FIXTURE.
The liquid in the trap can burn your skin.

  1. Look at the two nuts on the trap.
    <1m
NOTICE

LOOSEN THE NUTS ON THE TRAP BY HAND ONLY.
A tool can cause damage to a plastic nut.

  1. Loosen the two nuts by hand.
    1m
  2. Hold the trap with one hand. Lower the trap into the bucket.
    • The trap holds water and waste.
    <1m
  3. Remove the waste from the inside of the trap.
    <1m
  4. Clean the inside of the trap with the brush.
    2m
  5. Examine the two washers on the nuts.
    <1m
  6. Replace a washer that has damage.
    <1m
  7. Install the trap on the tailpiece and on the drain outlet.
    1m
  8. Tighten the two nuts by hand.
    <1m
  9. Open the water supply valve.
    <1m
  10. Run water into the fixture for one minute. Make sure that there is no leak at the two nuts.
    2m

Use the drain auger

Estimated 9 min

NOTEA drain auger is a flexible steel cable with a handle. Turn the handle clockwise only.
WARNING

PUT ON THE GLOVES BEFORE YOU TOUCH THE DRAIN AUGER.
The end of the auger is sharp and can cut your hand.

  1. Put the end of the drain auger into the drain outlet.
    <1m
  2. Push the auger into the pipe until you feel resistance.
    1m
  3. Turn the handle of the auger clockwise.
    <1m
  4. Continue to turn the handle. Move the auger deeper into the pipe.
    2m
  5. If the handle turns freely, the blockage is clear.
    <1m
  6. Remove the auger from the pipe slowly.
    1m
  7. If you removed the trap, install the trap again.
    2m
  8. Run water into the fixture for two minutes.
    2m
  9. If the water does not drain, stop. Speak to a plumber.
    <1m

After the job

Estimated 5 min

  1. Put the waste from the trap into the refuse bag.
    <1m
  2. Clean the tools with hot water and soap.
    2m
  3. Store the tools in a dry place.
    1m
  4. Remove the gloves. Wash your hands.
    1m
  5. Record the date of the work.
    <1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

trap
Also called: U-bend, P-trap, S-bend, gooseneck, the bendy pipe under the sink, sink trap
drain auger
Also called: drain snake, plumber's snake, sink snake, hand auger, plumbing snake, toilet snake
cup plunger
Also called: plunger, plumber's helper, sink plunger, force cup
blockage
Also called: clog, stoppage, backup, blocked drain, clogged drain, slow drain
waste pipe
Also called: drain line, drain pipe, branch line, waste line
stopper
Also called: plug, pop-up plug, pop-up stopper, drain stopper, sink plug
chemical drain cleaner
Also called: drain unblocker, caustic soda, lye, liquid drain opener

When to use a professional

Stop if all the drains in the building are slow at the same time. The blockage is then in the building drain. Speak to a plumber.

Stop if waste water is at a floor drain. Stop if waste water is outside the building. Stop if the fixture has a leak that you cannot stop. Speak to a plumber.

Do not use a chemical drain cleaner to clear a drain. Do not put a powered drain machine into a pipe. This page does not give a chemical dose. This page does not give a temperature limit for your pipe. Ask the manufacturer of the pipe for these values.

Common questions

How do I unclog a slow or blocked sink drain?

Start at the fixture, because that is where almost every household blockage sits. A cup plunger clears most of them in under a minute. The trap under the sink, the U-bend, is the next place to look, and cleaning it out by hand is often the whole repair. If the plunger and the trap both come up empty, a hand drain auger will reach the short run of pipe behind the wall. Beyond that you are into the building's drain, which is a plumber's job.

Should I use a chemical drain cleaner like Drano?

This page does not tell you to, and it will not print a dose or a contact time for one. Caustic drain cleaners are sodium or potassium hydroxide, and ATSDR describes direct contact with concentrated solutions as causing thermal and chemical burns leading to deep-tissue injuries, with severe eye damage in strong solutions. The Army's own plumbing manual makes a separate practical point: chemical cleaners have to reach the blockage to do anything, so they should not be used in a pipe that is already fully stopped. What happens instead is that the caustic liquid stands in the fixture, and then it is the thing you plunge, unscrew or splash. Mechanical clearing has none of those failure modes, which is why it is the whole of this page.

Why is one drain blocked but the others are fine?

Because the blockage is on that fixture's own branch, upstream of the point where it joins everything else. That is good news: it is the short, accessible part of the system, and it is the part this page covers. The Army plumbing course uses exactly this test to place a stoppage. One fixture affected means its own branch line, and every fixture affected means the main line.

What is the difference between a plunger and a drain snake?

A plunger moves the water in the pipe and breaks the blockage apart with it. A drain auger, the snake, is a flexible steel cable you feed down the pipe to reach the blockage physically. Try the plunger first: it is faster, it is cheaper, and it cannot scratch the inside of a trap. Use the auger when the plunger has had three honest attempts and the water still stands.

Every drain in the house is backing up at once. What does that mean?

It means the blockage is downstream of everything, in the building's main drain rather than in any one fixture. Nothing on this page reaches that. It is cleared through a cleanout with heavy equipment, and it is a plumber's job. If waste water is appearing at a floor drain or outside the building, stop using water in the house and call one now.

What is the U-bend under the sink, and why is it full of water?

That is the trap, and the water standing in it is a seal. It stops drain smells and insects coming back into the room, which is why a trap must never be left off overnight. It is also the narrowest and lowest point on the fixture's drain, so it is where hair and grease collect first. That is why cleaning it out by hand fixes so many slow drains.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 1TM 3-34.70 / MCRP 3-17.7E, Plumbing, Pipe Fitting, and SewerageHeadquarters, Department of the Army (Army Publishing Directorate) · accessed 2026-07-29 · re-verification due 2027-01-25
  2. Tier 1Medical Management Guidelines for Sodium HydroxideAgency for Toxic Substances and Disease Registry (ATSDR), Centers for Disease Control and Prevention · accessed 2026-07-29 · re-verification due 2027-01-25
  3. Tier 1NIOSH Pocket Guide to Chemical Hazards — Sodium hydroxideNational Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 1 · updated 2026-07-29 · next review due 2027-07-29

  1. v1 · 2026-07-29First draft. Built from the owned document drive: US Army subcourse EN5115 (2004) ingested with scripts/manuals.py --add-local, registered at tier 2 because no publisher-hosted copy exists online. Task breakdown and step sequence taken from that document; every sentence written independently in Simplified Technical English. Sequence re-confirmed against TM 3-34.70 (2012, armypubs.army.mil), which superseded the doctrine the subcourse was derived from.

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

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