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Quick answer: A discharge-pipe weep hole lets trapped air escape so a pump can move water. Whether to drill one, its size and its position depend on the exact pump. The Zoeller M53 and Wayne CDU980E examples below require different choices. A built-in vent alone does not settle the question.
Repair before replacing: a pump that runs without lowering the water level may be air locked, but a blocked discharge, backwards check valve or another fault can produce similar symptoms. Diagnose the cause before buying a replacement; see sump pump troubleshooting. If replacement is necessary, our sump pump guide compares the exact models and installation requirements below.
Does your pump need a weep hole? Two model examples
| Pump | Discharge vent guidance |
|---|---|
| Zoeller M53 | Approximately 3/16 inch below the check valve and basin cover. Its housing vent does not replace the additional recommended discharge vent. |
| Wayne CDU980E | The maker’s model page says no weep hole is needed because of its top-suction design. Use that model’s installation instructions. |
Zoeller FM2676, page 1, caution 3 covers the M53’s vent requirement and a separate high-head exception. Page 3 shows the installation. Do not apply the exception without following its conditions or an installer’s guidance. Wayne’s CDU980E product page supplies the no-weep-hole statement; the current sump installation manual, page 4 still requires a check valve.
These are two examples, not a rule for every Zoeller or Wayne pump. Check the nameplate and the instructions supplied with your exact model and version before altering its discharge pipe.
What an air lock can look like
- The motor runs, but the pit’s water level does not fall normally.
- The problem may appear after a dry basin or a pump installation.
- Trapped air can stop the pump from developing the pressure needed to move water through the check valve.
This symptom does not prove the motor and impeller are healthy. Zoeller’s service checklist also lists clogged piping or strainer, excessive discharge head and other causes of little or no flow. Follow the model’s troubleshooting procedure rather than drilling a hole as a universal cure.
Where does the hole go, if your manual requires one?
Follow the model’s specified discharge-pipe location and diameter. It must relieve the pump side of the check valve; a hole above that valve cannot vent trapped air below it. Keep the discharge stream contained within the basin as the instructions require.
Boshart’s general weep-hole guidance gives about 5 inches above the pump connection and below the check valve as an example. That is not a universal pump dimension, and the article does not specify a hole diameter. The exact pump manual takes priority.
Before handling the pump or discharge assembly, disconnect power as the maker instructs. Do not handle a powered pump while standing in water. If the area is flooded or access is unsafe, get qualified help rather than reaching into the basin.
Check the vent and check valve before replacing the pump
On an installation that requires a vent, check it for clogging at the interval the maker recommends. An oversized hole is not a substitute for a blocked one; changing the diameter can divert more water back into the basin. A stream from a correctly specified vent during operation can be normal.
Check the valve’s flow arrow against the discharge direction. A backwards valve can obstruct flow, while a failed or missing one can let water drain back after the pump stops. Those faults need diagnosis and repair; a stronger new pump does not fix the wrong piping arrangement.
If water is not moving, stop repeated testing and follow the maker’s service guidance. Zoeller directs unresolved problems to an authorized service center. Avoid assuming that every strong spray, long run or slow drawdown proves the hole is the wrong size.
The winter version of this problem
A vent hole does not clear a frozen discharge line. If the outside route is blocked by ice, address the discharge arrangement; drilling another hole or replacing a working pump misses the cause.
Frequently asked questions
Where do you drill a weep hole in a sump pump discharge pipe?
Use the location in your exact pump’s instructions. When a discharge vent is required, it belongs on the pump side of the check valve and must return water safely to the basin. Boshart’s 5-inch example is not a universal dimension.
Do all sump pumps need a weep hole?
No. The two model examples above differ, and a built-in air-relief feature alone is not permission to skip the exact installation instructions.
My sump pump runs but no water moves. Is that an air lock?
It may be, but blocked piping, a backwards check valve, excessive discharge head or a pump fault can also reduce flow. Follow the model’s troubleshooting instructions before drilling or buying another pump.
How big should the weep hole be?
Use the exact model’s instructions. The described M53 installation uses approximately 3/16 inch; that dimension is not a universal answer.
Is water squirting out of the hole normal?
A stream returning to the basin while a correctly specified vent operates can be normal. Spray outside the basin or poor pump performance needs inspection; the stream alone does not prove that the hole is oversized.
Sources
- Zoeller FM2676, revision 0726: pages 1–3, vent guidance and service checklist.
- Wayne CDU980E model page: top-suction design and no-weep-hole statement.
- Wayne 600002W-001 J, revision 06/25: page 4, check valve and installation.
- Boshart weep-hole article: general purpose and location example, not a model-specific diameter.