Install the check valve on the discharge line, between the pump and where the pipe exits your foundation

The check valve goes on the pipe that carries water out of your sump pit—not inside the pit itself. It sits on the vertical or horizontal section of discharge pipe after the pump but before the pipe leaves your basement or crawlspace. Most homeowners install it within 3 to 5 feet of the pump, though the exact distance depends on your setup.

The purpose is straightforward: the check valve lets water flow out when the pump runs, then closes to stop water from flowing backward into the pit when the pump shuts off. Without it, water that has already been pumped out can drain back down into the pit, forcing the pump to run again unnecessarily and wearing it out faster.

Key Takeaways

  • Install the check valve on the discharge pipe between the pump and the foundation wall, typically within 3 to 5 feet of the pump outlet.
  • The valve must be oriented so water flows in the correct direction—check the arrow on the valve body to match the direction water travels.
  • A horizontal section of pipe is easier to work with than a vertical one, but either location works if the valve is installed correctly.
  • If your pump already has a built-in check valve, you may not need a separate one, though some plumbers add a second valve for extra protection.

Why distance from the pump matters

Placing the check valve close to the pump—within a few feet—means water doesn't sit in the discharge pipe between the pump and the valve when the pump stops. If the valve is too far away, that trapped water can create a column of weight that stresses the pump and can cause it to work harder on the next cycle.

However, the valve doesn't have to be right at the pump outlet. Many installations place it 3 to 5 feet away to give you room to work if you ever need to service the pump. The key is keeping it reasonably close rather than running 20 or 30 feet of pipe before the valve kicks in.

Vertical versus horizontal pipe orientation

If your discharge pipe runs vertically up the wall, you can install the check valve anywhere along that vertical section. If it runs horizontally across the basement floor or along the wall, the valve can sit on that horizontal run. Most people find horizontal pipe easier to work with because you don't have to support the valve's weight while you're installing it.

The orientation of the valve itself matters more than whether the pipe is vertical or horizontal. The valve body has an arrow printed on it showing the direction water should flow. That arrow must point toward the outside of your home—in the direction the pump pushes water. If you install it backward, water won't flow out at all.

Checking if your pump already has a built-in check valve

Some sump pumps come with a check valve already attached to the pump outlet. If yours does, you may not need to install a separate one. Look at the pump discharge fitting—if there's a valve body with an arrow right where the pipe connects, you have a built-in valve.

Even if your pump has a built-in check valve, some plumbers recommend adding a second check valve further up the discharge line as backup protection. This is optional and depends on how concerned you are about backflow and how often your pump runs. A single check valve is the standard installation; a second one is insurance.

How to position the valve for proper water flow

Before you install the valve, hold it up to the discharge pipe and look for the arrow on the valve body. The arrow should point in the same direction the water travels—away from the pit and toward the outside. If you're unsure which way water flows, remember that the pump pushes water out, so the arrow should point away from the pump.

Once you've confirmed the direction, you can install the valve using the threaded fittings on both ends. Most check valves screw onto standard PVC or metal discharge pipes. Wrap the threads with plumber's tape (also called PTFE tape) before screwing the valve on to create a watertight seal. Tighten by hand first, then use a wrench to snug it down—don't over-tighten, which can crack the valve body.

Common mistakes that cause check valve problems

The most common error is installing the valve backward. Water will not flow out if the arrow points toward the pump instead of away from it. If your pump runs but no water comes out, the first thing to check is the valve orientation.

Another mistake is installing the valve too far from the pump—say, 15 or 20 feet away on a long discharge line. While this won't prevent the valve from working, it means a lot of water sits in the pipe between the pump and the valve, which can create backpressure and wear on the pump. Keeping it within 5 feet solves this.

A third issue is forgetting to use plumber's tape on the threads. Without it, the connection can leak slowly, and water may drip back into the pit around the valve rather than flowing through it. This defeats the purpose of having the valve.

When to call a plumber for check valve installation

If your discharge pipe is already in place and you're comfortable working with basic plumbing fittings, you can install a check valve yourself in about 15 minutes. If you're unsure about the pipe layout, the direction of water flow, or how to make a watertight connection, a plumber can do it quickly and inexpensively.

You should also call a plumber if your pump is not pushing water out at all and you suspect a check valve problem. They can test the valve, confirm it's installed correctly, and replace it if it's stuck or damaged. A stuck check valve is one of the most common reasons a sump pump stops working.

Frequently Asked Questions

Can I install a check valve on a horizontal discharge pipe instead of vertical?

Yes. A horizontal pipe is often easier to work with because you don't have to support the valve's weight while installing it. The valve works the same way on horizontal or vertical pipe as long as the arrow on the valve body points in the direction water travels.

What happens if water flows backward into the sump pit?

Without a check valve, water that has been pumped out can drain back into the pit when the pump stops. This forces the pump to run again to remove the same water, which wears out the pump faster and wastes electricity. A check valve prevents this by closing automatically when the pump shuts off.

Do I need a check valve if my pump has one built in?

A built-in check valve is usually enough for standard residential use. Some plumbers add a second check valve further up the discharge line as extra protection, but this is optional. One valve is the normal installation.

How do I know which way the arrow on the check valve should point?

The arrow should point in the direction water travels—away from the sump pit and toward the outside of your home. If you're unsure, remember that the pump pushes water out, so the arrow points away from the pump outlet.

What should I do if my pump runs but no water comes out?

Check the check valve first. It may be installed backward, stuck, or clogged. If the arrow points toward the pump instead of away from it, turn off the pump and reinstall the valve in the correct direction. If the valve is in the right direction but water still won't flow, the valve may be damaged and need replacement.