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

Cleaning a Sump Pit and Checking the Check Valve

Removing debris and sediment from the pit, and testing the discharge check valve for backflow
ApplicabilityDomestic submersible sump pumps with a discharge check valve, in a basement or crawl space sump pit
Task time22 min to 31 min editorial estimate, not a measurement
PersonnelOne
Revisionv1 · 2026-08-04
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 sump pit collects ground water, and over months it also collects the things ground water carries: fine sediment, and sometimes gravel that has worked its way in around the liner. None of that is a fault. It is what a hole in a basement floor does. The other half of this page is the part of the sump system a simple fill test does not reach: the discharge check valve, a one-way fitting on the pipe above the pump that is supposed to stop water already pushed up the pipe from running straight back down into the pit the moment the pump switches off. Liberty Pumps' own installation manual lists a check valve that will not close as a documented cause of a pump that cycles every minute or runs when nobody has used a fixture, because the pump keeps re-pumping water that just fell back in.

This page cleans the pit and checks that valve. It does not replace the fill test on Testing a Sump Pump, and it does not cut or reglue the discharge pipe: opening the check valve here only applies where the installation already has a union, the kind of fitting a pump maker installs so the valve can be freed by hand rather than by a saw. Where there is no union, or the check valve will not come free, the page stops and sends the reader to a plumber or a pump dealer rather than guessing with a hacksaw.

Safety

WARNING

DO NOT TOUCH THE PUMP, THE CHECK VALVE OR THE WATER WHILE THE PUMP HAS ELECTRICAL POWER.
Contact with an electrical part through water can kill you.

Necessary equipment

ItemNote
Rubber glovesThe gloves must cover your wrists.
BucketUse a bucket that holds at least 10 litres.
FlashlightA sump pit is dark even with the cover off.
Old towelsThe towels absorb water on the floor.
Adjustable pliersUse the pliers only if the union nut does not turn by hand.
Small stiff brushUse the brush to clean the check valve and the vent hole.
Notebook or maintenance recordRecord the date of this task.
Clean water materialWater from a tap is enough for the test.

Prepare the area

Estimated 3 min to 5 min

NOTEA sump pit is a hole that collects water from the ground. The water can carry bacteria.
WARNING

PUT ON THE GLOVES BEFORE YOU TOUCH THE SUMP PIT OR THE CHECK VALVE.
Water in the pit can carry bacteria that cause illness.

  1. Put on the rubber gloves.
    <1m
  2. Find the sump pit in the basement or the crawl space.
    1m
  3. Put the old towels around the sump pit.
    <1m
  4. Remove the cover from the sump pit.
    • The cover keeps debris out of the pit.
    • The cover prevents an accidental fall into the pit.
    <1m

Disconnect the electrical power

Estimated under a minute

NOTEPump makers say to disconnect the pump from its power source before you handle it.
WARNING

DISCONNECT THE PUMP FROM THE OUTLET BEFORE YOU PUT YOUR HAND INTO THE SUMP PIT.
The pump can start without warning and injure your hand.

  1. Disconnect the pump from the outlet.
    <1m
WARNING

DO NOT TOUCH THE PLUG WITH WET HANDS.
Water on your skin can cause a fatal shock.

  1. Make sure that your hands are dry.
    <1m
  2. Make sure that the floor around the outlet has no water on it.
    <1m

Remove the pump from the pit

Estimated 1 min

NOTESome pump makers do not allow you to lift the pump by hand. Read your pump documentation before you lift the pump.
Whether the pump may be lifted from the pit by its handle
Unverified — do not rely on this value
READ THE PUMP DOCUMENTATION BEFORE YOU LIFT THE PUMP

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

  1. Look at your pump documentation before you lift the pump.
    • Some pump makers do not allow you to lift the pump by hand.
    <1m
WARNING

NEVER LIFT THE PUMP BY ITS POWER CORD.
A torn cord can expose live wires and cause a shock.

CAUTION

LIFT THE PUMP WITH YOUR LEGS, NOT YOUR BACK.
A full pump is heavy and can strain your back.

  1. Grasp the pump by its handle, not the cord.
    <1m
  2. Lift the pump out of the sump pit.
    <1m
  3. Set the pump on the towels.
    <1m

Clean the sump pit

Estimated 6 min to 10 min

NOTEGround water can carry sediment, gravel and other debris into the pit over time.
Sump pit diameter
Unverified — do not rely on this value
MEASURE YOUR OWN SUMP PIT OR CONSULT THE INSTALLATION DOCUMENTATION

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

  1. Look into the sump pit with the flashlight.
    <1m
CAUTION

EXAMINE DEBRIS FOR SHARP EDGES BEFORE YOU PICK IT UP BY HAND.
A sharp edge can scrape your skin.

  1. Remove stones, gravel and other debris from the pit.
    2m
  2. Scoop loose sediment from the bottom of the pit into the bucket.
    2m
  3. Wipe the inside walls of the pit with a cloth.
    1m
  4. Examine the pit liner for cracks or holes.
    <1m

Examine the discharge check valve

Estimated 4 min to 6 min

NOTEA check valve closes when the pump stops. It stops backward flow of water into the pit.
Check valve type and size
Unverified — do not rely on this value
CONSULT THE MANUFACTURER DOCUMENTATION FOR YOUR CHECK VALVE

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

  1. Find the check valve on the discharge pipe above the pump.
    <1m
  2. Look for a union near the check valve.
    • A union is a fitting with a large nut that separates by hand or with pliers.
    <1m
NOTICE

DO NOT FORCE A UNION NUT THAT WILL NOT TURN.
Force on a stuck nut can crack the fitting.

NOTICE

OPEN THE UNION OVER THE BUCKET.
Water trapped above the check valve can spill when you open the union.

  1. Loosen the union nut.
    <1m
NOTICE

NOTE THE DIRECTION OF THE CHECK VALVE BEFORE YOU REMOVE IT.
A check valve in the wrong direction can block the flow of water.

  1. Separate the union and slide the check valve free of the pipe.
    <1m
  2. Empty the check valve into the bucket.
    <1m
  3. Examine the inside of the check valve for stuck or damaged parts.
    <1m
  4. Rinse the inside of the check valve with clean water.
    <1m
NOTICE

DO NOT BLOCK THE VENT HOLE IN THE DISCHARGE PIPE.
A blocked vent hole can trap air and stop the pump.

  1. Clean debris from the vent hole below the check valve.
    • The vent hole releases trapped air from the pipe.
    <1m
  2. Install the check valve in the union.
    <1m
  3. Tighten the union nut by hand.
    • Use the pliers only if the nut does not seal by hand.
    <1m

Put the system back together

Estimated under a minute

  1. Put the pump back into the sump pit.
    <1m
  2. Connect the pump to the outlet.
    <1m

Run the check valve test

Estimated 4 min to 5 min

NOTEA pump that restarts with no new water in the pit shows a check valve that does not hold.
  1. Pour water slowly into the sump pit.
    1m
  2. Continue to pour water until the float rises and the pump starts.
    2m
  3. Do not add more water after the pump starts.
    <1m
  4. Watch the pump after the water level drops and the pump stops.
    <1m
  5. Listen for the pump to start again within the next minute.
    • A pump that starts again with no new water shows a check valve that does not hold.
    <1m

After the job

Estimated 3 min

Interval to inspect the sump pit and the check valve
Manufacturer or standard verified
3 months

Source: Installation Instructions, Recommended Models (form FM2676, P/N 151797-B) · tier 1 · accessed 2026-08-04

  1. Install the cover on the sump pit.
    <1m
  2. Make sure that the plug of the pump is fully in the outlet.
    <1m
  3. Remove the gloves. Wash your hands.
    1m
  4. Record the date of this task.
    <1m
  5. Do this task again after three months.
    <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.

sump pit
Also called: sump basin, sump hole, sump well, crock, the hole in the basement floor, sump pit full of gravel
sump pump
Also called: basement pump, cellar pump, water pump in the basement, sub pump, submersible pump, clean sump pump
check valve
Also called: one way valve, non-return valve, backflow valve, check valve sump
discharge pipe
Also called: discharge line, outlet pipe, sump pump pipe, drain line
union
Also called: union fitting, union coupling, pipe union
float switch
Also called: float, float ball, tether switch, level switch, bobber

When to use a professional

Stop if there is no check valve or union on the discharge pipe. Stop if the union will not loosen by hand or with the pliers. Stop if the check valve will not come free after you loosen the union. Call a plumber or a pump dealer.

Stop if the pump restarts often with no new water in the pit. Stop if the pit has a sewage smell. Stop if the pit refills with gravel a short time after you clean it. Speak to a licensed plumber.

Do not open the pump. Do not remove the base of the pump. The pump makers say that an authorized service center must do a repair. Do not cut or reglue the discharge pipe. Do not add a check valve to a pipe with none installed.

Never work in a wet basement while the equipment has electrical power. Speak to a licensed electrician about the outlet that supplies the pump.

Common questions

Why does my sump pump run every minute even when it hasn't rained?

That is the pattern Liberty Pumps' own troubleshooting table gives for a check valve that is not installed, is stuck open, or is leaking: water in the pipe falls back into the pit as soon as the pump stops, the float rises again, and the pump restarts to pump the same water a second time. Liberty's fix is short and direct: install a check valve, or remove the one that is there and examine it for free movement and correct installation. The listening test on this page — does the pump start again within a minute with no new water added — is how you find out which case you have.

My sump pit is full of gravel or sediment. Is that normal?

Some sediment is normal. Ground water carries fine material into an open pit over months, and Zoeller's own installation instructions list a clean, debris-free basin as a condition of a correct installation, not a one-time step. If the pit refills with gravel again soon after you clean it, that points at a crack or a gap in the pit liner rather than ordinary ground water, and it is worth a look before you clean it out a second time.

What does the check valve on a sump pump actually do?

It is a one-way fitting on the discharge pipe, and Liberty Pumps' installation manual states its purpose plainly: "A check valve is required just above or in place of the union to prevent the backflow of liquid after each pumping cycle." Without it, water already pushed up the pipe falls straight back into the pit the moment the pump stops.

How do I know if my check valve has failed?

Watch and listen after a normal cycle. Liberty Pumps' troubleshooting table lists "check valve stuck closed or installed backward" as a cause of a pump that starts and stops too often, and "check valve not installed, stuck open, or leaking" as a cause of a pump that cycles too frequently or runs when nobody has used a fixture. The remedy in both cases is the same, in the manual's own words: "remove check valve and examine for freedom of operation and proper installation."

My sump pit smells bad. What should I do?

A pit that only ever holds ground water should not smell like sewage. Zoeller's installation instructions are explicit: "Dewatering and effluent sump pumps are not designed for use in pits handling raw sewage." A musty smell after cleaning is usually standing water or old sediment and goes away with the clean this page describes. A sewage smell is a plumbing problem, not a cleaning problem, and belongs to a plumber.

Does every sump pump need a check valve?

Zoeller's own dos-and-don'ts list tells the installer to "install a check valve and a union in the discharge line," and Liberty Pumps calls a check valve required to stop backflow after each cycle. If your installation has neither a check valve nor a union, adding one means cutting into the discharge pipe, which this page does not cover — that is a job for a plumber or a pump installer.

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 1Installation Instructions, Recommended Models (form FM2676, P/N 151797-B)Zoeller Pump Company · accessed 2026-07-29 · re-verification due 2027-01-25
  2. Tier 1Installation Manual — S30-Series Submersible Sump Pumps (document 7175000H)Liberty Pumps, Inc. · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 1 · updated 2026-08-04 · next review due 2027-08-04

  1. v1 · 2026-08-04First draft. Built from the two manufacturer documents already registered in data/sources.json for this backlog entry: the Zoeller FM2676 installation instructions and the Liberty Pumps S30-Series installation manual, both fetched and read directly from the publishers' own sites again on 2026-08-04 and extracted with the repository's standard-library pdftext extractor. Every step written independently in Simplified Technical English from the meaning of those documents, not from their wording. The check-valve work is limited to a union already present in the installation: no step cuts or solvent-welds the discharge pipe, and a missing union or a check valve that will not free routes to a plumber in the professional boundary. Three per-unit values route to the reader's own documentation rather than publishing a guess: pit diameter, check valve type and size, and whether the pump may be lifted from the pit by its handle. The one verified specification, the three-month inspection interval, reuses the figure already verified for data/procedures/test-a-sump-pump.json against the same Zoeller source, with its own access_date recorded for this record. Both sources were already admitted to data/sources.json by a prior session, so data/sources-additions-clean-a-sump-pit-and-check-the-check-valve.json is staged empty.

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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