The water drains to the ground or storm sewer outside your home

A sump pump moves water from the pit in your basement to somewhere it won't come back inside. That somewhere is usually one of three places: the ground next to your house, the municipal storm sewer system, or (less often) the sanitary sewer. The pump sits in a basin below your basement floor, collects groundwater seeping in, and when the water reaches a certain level, a float switch triggers the pump to turn on and push the water out through a discharge pipe.

The discharge pipe is the key. It runs from the pump up through your basement wall or rim joist and then outside. Where it empties depends on what your local code allows and what your home's plumbing setup is. Most homeowners have a choice, but some municipalities have rules about which option you must use.

Key Takeaways

  • Sump pump discharge most commonly goes to the ground at least 4 to 10 feet away from your foundation, depending on your local code.
  • Some municipalities require discharge into the storm sewer system instead of the ground, so check your local building department before choosing.
  • Discharging into the sanitary sewer is rarely allowed and usually only permitted when no other option exists.
  • The discharge pipe should be buried, sloped downward, and have a check valve to prevent water from flowing backward into the pump.
  • If your pump discharges to the ground, the outlet should be above grade so water doesn't pool and seep back into the foundation.

Discharging to the ground around your foundation

This is the most common setup. The discharge pipe runs out of your basement and empties onto the ground surface or into a buried pipe that extends away from your house. The goal is to move water far enough away that it won't seep back through your foundation or pool against your basement wall.

Most codes require the discharge point to be at least 4 to 10 feet from your foundation—the exact distance varies by municipality. Some areas specify that water must drain away from the house at a slope of at least 1 inch per 8 feet. If the pipe is buried underground, it typically ends above grade (above the soil surface) so water can flow out and away rather than pooling.

A common mistake is letting the discharge outlet sit at ground level or below it. Water will pool there and either evaporate slowly or seep back toward the foundation, defeating the whole purpose. The outlet should be visible and positioned so water flows downhill and away from your home.

Discharging into the storm sewer

Many municipalities have a separate storm sewer system designed to handle rainwater and groundwater runoff. If your area has one, your local code may require or allow you to tie your sump pump discharge into it instead of letting water drain across your yard.

To do this, the discharge pipe connects to a storm drain inlet, usually located in the street or alley. You will need a permit from your city or county before making this connection, and the work often requires a licensed plumber because the connection point and pipe sizing are regulated. Some areas charge a small fee for the permit or for connecting to the storm system.

The advantage is that you don't have to worry about water pooling near your foundation or running across your neighbor's property. The disadvantage is that you lose control of where the water goes once it enters the municipal system, and you may be liable if the connection is improper and causes flooding elsewhere.

Discharging into the sanitary sewer (rarely allowed)

The sanitary sewer carries wastewater from toilets, sinks, and showers to the treatment plant. Most municipalities do not allow sump pump discharge into the sanitary sewer because it adds volume that the system wasn't designed to handle, especially during heavy rain when the pump runs continuously.

In rare cases—usually when a home has no storm sewer access and the ground is too wet or too close to the water table to allow ground discharge—a municipality may permit sanitary sewer discharge. If this is your only option, you will need a permit and the connection must be made by a licensed plumber. Some areas require a separate check valve and a cleanout to prevent backflow.

What happens inside the discharge pipe

The discharge pipe itself needs to be sized correctly and installed with a slight downward slope so water flows out and air doesn't get trapped inside. Most residential sump pumps use 1.25-inch or 1.5-inch PVC pipe, though the size depends on the pump's flow rate.

A check valve is almost always installed in the discharge pipe, usually right where it exits the pump or the basement wall. This one-way valve lets water flow out but prevents it from flowing backward into the pit when the pump shuts off. Without a check valve, water would drain back into the basin and the pump would cycle on and off constantly, wearing out faster.

The pipe should be buried or routed so it's not a tripping hazard and doesn't freeze in winter. In cold climates, the discharge outlet should be positioned so water doesn't pool and freeze at the end of the pipe, which could block future discharge. Some homeowners install a frost-proof sillcock or a valve that lets them cap the outlet in winter.

Checking your current discharge setup

If you already have a sump pump, you can trace where it drains by following the discharge pipe from the pump. Look for where it exits your basement—through the rim joist, the foundation wall, or the floor—and then follow it outside to see where the water comes out.

If the outlet is right against your foundation or pooling water near the basement wall, that's a sign the discharge is not far enough away. If the pipe is buried and you can't see the outlet, you may need to dig or ask a plumber to locate it. If you're unsure whether your setup meets current code, contact your local building department or a licensed plumber for an inspection.

When to call a professional

If you're installing a new sump pump or relocating the discharge, a licensed plumber should handle the work, especially if it involves connecting to the storm sewer or sanitary sewer. These connections require permits and must meet code, and mistakes can lead to flooding, property damage, or fines.

If your pump is discharging in a way that causes water to pool near your foundation, seep into a neighbor's yard, or freeze at the outlet, a plumber can reroute the pipe or extend the discharge line. This is usually a straightforward job but worth doing right so the water actually leaves your property instead of coming back.

Frequently Asked Questions

Can I discharge my sump pump into my downspout or gutter?

No. Downspouts and gutters are designed to handle roof runoff, not the continuous flow from a sump pump. The pump will overwhelm the gutter system, cause overflow, and water will run down the side of your house and pool against the foundation. The sump discharge must have its own separate path away from the house.

What if my yard is too wet to discharge water on the ground?

If the ground is saturated or your water table is very high, ground discharge may not work because the water won't drain away. In this case, you will likely need to connect to the storm sewer if your municipality has one, or ask your local building department what alternatives are allowed. A plumber can assess whether ground discharge is viable for your property.

Does the discharge pipe need to be buried?

It doesn't have to be, but it's usually a good idea. A buried pipe is out of the way, less likely to freeze in winter, and looks neater. If the pipe is above ground, it should be sloped downward, secured so it doesn't move, and positioned where it won't be a tripping hazard. The outlet should still be at least 4 to 10 feet from the foundation.

What if water comes back into the sump pit after the pump shuts off?

That's a sign the check valve is stuck or missing. Water should not flow backward into the pit. If it does, the pump will cycle on and off constantly and wear out quickly. Have a plumber inspect the check valve and replace it if it's faulty or install one if it's missing.

Can I cap the discharge outlet in winter?

You can cap it temporarily to prevent freezing, but you must remove the cap before the pump runs again. If the pump tries to discharge into a capped pipe, pressure will build up and the pump can fail or the pipe can burst. Some homeowners install a frost-proof outlet or a valve that automatically opens when the pump runs, so they don't have to remember to uncap it.