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Do Sump Pumps Need Weep Holes?

Do Sump Pumps Need Weep Holes?
Do Sump Pumps Need Weep Holes?

Ahh, the wonderful world of Sump Pumps. Those pesky little things in your deep, dark basement that we only ever think about when they stop working. Though I would say we likely don’t think about our A/C, Furnace, Water Heater, or Water Softener before they go out either. Beyond them existing, we don’t think about how they work much at all. And most of the time, you don’t need to know. The important thing is that they work.

However, if you have an inquisitive mind, read on….

Basic Operation of Sump Pump

A Sump Pump operates on simple physics. A water-cooled motor is housed inside a (if properly built) cast iron or stainless-steel casing. This motor moves a propeller at the base of the pump, pushing water up through the pipe. Imagine a plane propeller facing the ground, pushing all the air straight up. Same concept, but with water and your basement.

This water is pumped through a 1.5” or 2” pvc pipe, passing a 1-way check valve, and runs outside your house and into the yard or storm sewer system. The basic concept being that as long as the Sump Pump can keep the water in the basin discharged, it can keep the water level under your floor, and your basement dry.

Read also – How Submersible Sump Pumps Work?

Weep Holes

Alright, now for the confusing part. In the pvc pipe described above, between the pump and the 1-way check valve, there needs to be what is called a “weep hole” in the pvc. This is a 1/8” hole drilled at an upward angle. Now, why would anyone drill a hole in a pipe they are discharging pressurized water through?

The answer is Air Lock. Weep Holes prevent Air Lock in your Sump Pump. Dumbed down a bit more, think a bubble of air surrounded by water on both sides. This “bubble” of air causes a change in pressure that does not allow the pump to push water through the pipe. It simply doesn’t have the power.

Compare to Brakes

Have you ever done brakes on your car? Do you know about how we need to “bleed” the brake lines in order to make them effective? This is much the same concept, as air in the brake lines do not allow you to put enough pressure to activate the brakes through the pedal.

An air bubble in your Sump Pump line will cause “Air Lock” and prevent your pump from pumping the water effectively out of your home.

Easy Installation

Installing a Weep Hole in your Sump Pump is easy. You simply take a 1/8” drill bit and drill. Once you have your initial Sump Pump assembly together with the pvc piping installed, you then drill the hole (Pump OUT of the pit, as you will find this makes it far easier).

It is important to start this hole about 6” above the Sump Pump, and to drill it at a 45-degree angle UPWARDS. This will allow the water that will inevitably shoot out of this hole to be directed downwards. You will slap your own forehead when you install this hole at a downward angle and water is spraying up and out of the pit every time the pump goes off.

Thanks for reading, and as always:

“Not Everything’s Better When Wet”


Austin Werner

Austin Werner is the Owner of The Real Seal LLC, a basement waterproofing and foundation repair company. Austin believes that having a highly trained and happy team is the key to success. This is reflected through hundreds of 5 star customer reviews his company has received online.

10 Responses

    1. Hi Vince!

      Best not to put a weep hole that high. You’re likely to get spray up over the pit lid. The most effective placement of the weep hole is a few inches above the connection the sump pump. You also want to angle that hole downwards so the spray from the water goes down to the bottom of the pit. Hope this helps!

  1. In 15 years of servicing and installing sump pumps never once Have I received a call for an air locked Home Depot sump pump. But I have opened plenty of crocks to check the pump or water flow and PSSSSSSS water everywhere.
    Unscrewed a crock lid once just as the pump kicked on. Customer was standing across from me and took that “downward” spray from knee to face! I guess the original call was for sewage back up. The second call was to another contractor.
    Beware the PEE hole!!

    1. Hahaha beware the pee hole! Yes, it is very important that when the weep hole is drilled that it is drilled upwards into the pipe, allowing the water to spray down into the pit. Air lock in sump pumps is a real thing and it is not only standard installation procedure for the industry, but also standard installation procedure straight from the manufacturer.

  2. Zoeller recommends this hole to be drilled at the level of the top of the sump pump but when I learned this I had already installed piping and the check valve from the pump. Can this hole be drilled to high or too low for functional reasons? Thankyou!

    1. Hi Randal!

      That is a great question. We also recommend the weep hole be installed at the top of the sump pump (or about 12″ from the bottom of the pipe). The reason for this is to allow the water to drain out of the pipe below the check valve to prevent something called “air lock.” Odd phenomenon, but your pump can actually lock up if there is pressure/water in that section below the check valve.

      So having the hole as far down as possible is the best scenario, but we have seen them work halfway up the pipe as well. We would not recommend them be drilled higher, as it would defeat the purpose and also likely end up spraying water outside of the pit when the pump is triggered.

      Hope this helps!

  3. Since I have a back up sump pump, I also have a check valve connected right above my primary sump pump to keep water back charging thru the primary when the back up sump pump is on. I also have the check valve outside of the sump pump. My question is this: Should I drill my weep hole “under” that bottom check valve to prevent vapor lock? If I drill the weep hole in the PVC pipe between the 2 check valves I’m guessing that will not prevent vapor lock.

    1. Hi Pete!

      From the sound of it, you have a sump pump, battery backup, and a check valve for each. In this case, you will want the weep hole on both pipes beneath the check valves. Best location for it is about 8″ or so above the bottom of the pipe where it goes into the sump pump itself.

  4. I have a Zoeller sump pump and just recently noticed that it will not shut off once the float goes down and the switch kicks off. Also, after the pit is basically empty, water shoots out of a little hole that’s built into the side of the base of the pump; this hole is not the weep hole drilled into the side of the vertical PVC discharge pipe. The hole in the side of the pump base is exposed because the pump eliminates most of the water from the pit because it doesn’t shut off. Do you know what would cause water to shoot out of this hole, and does it have anything to do with the pump not shutting off?

    1. Hi Rodney!

      Some Zoeller sump pumps have weep holes already built into them. You’d be surprised, but there are many licensed plumbers and waterproofers who do not know, or outright refuse, to install the weep holes. So some sump pump manufacturers combat this by installing them in the pump themselves during production.

      Your float switch is completely separate from the weep hole issue. Zoellers are great pumps, but notorious for their float switches failing. The fix for this is to have the float switched replaced. Depending on the life of the pump, it may be more economical to swap the entire pump out altogether. If the pump is more than 5 years old, we would recommend swapping the pump out for a new one.

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