What plumbing connections a pressure tank needs
A water pressure tank connects to your home system at four points: the main water line coming in, the line going out to your house, the air valve on top, and a drain at the bottom. The tank sits between your water source (a well pump or municipal line) and your home's pipes, so water flows in from the source, the tank stores it under pressure, and your home draws from the tank as needed.
The incoming line attaches to a check valve first—this one-way valve prevents water from flowing backward into your source. From there, a line runs into the tank's lower inlet port. The outgoing line connects to the tank's upper outlet port and runs to your home's main water line. The air valve (usually a Schrader valve, like a tire valve) sits on top and lets you adjust the air pressure inside the tank. A drain valve at the very bottom lets you empty the tank for maintenance.
Most residential tanks range from 20 to 80 gallons and mount either vertically or horizontally depending on your space. Vertical tanks are more common in basements or utility rooms; horizontal tanks fit in tight crawl spaces. The tank itself is a steel or composite shell with a rubber bladder inside that separates air from water.
Key Takeaways
- Water enters through the lower inlet port after passing through a check valve, and exits through the upper outlet port to supply your home.
- The air valve on top controls the air pressure inside the tank, which should be set to about 2 pounds per square inch below your pump's cut-in pressure.
- All connections use threaded fittings (usually 3/4-inch or 1-inch NPT) with thread seal tape and pipe dope to prevent leaks.
- The drain valve at the bottom must connect to a floor drain or sump so water does not pool under the tank.
- Pressure gauges on both the incoming and outgoing lines help you monitor system performance and spot problems early.
Gathering the fittings and materials you will need
Before you connect anything, you need the right fittings for your tank's ports. Check your tank's manual or the port labels on the tank itself—most residential tanks have 3/4-inch or 1-inch NPT (National Pipe Thread) ports. You will need brass or stainless steel fittings because they resist corrosion better than galvanized steel, especially inside a pressure tank.
For the inlet side, buy a check valve rated for your system's pressure (usually 40 to 60 pounds per square inch), a tee fitting to branch off to a pressure gauge, and a ball valve to isolate the tank for maintenance. For the outlet side, use another ball valve and a pressure gauge. Get thread seal tape (white PTFE tape) and pipe dope (a paste sealant) for every threaded connection—tape alone is not enough on pressure fittings.
You will also need two adjustable wrenches (one to hold the fitting, one to turn the connector), a bucket for catching water during assembly, and a tire pressure gauge or digital pressure gauge to set the air valve. If your tank does not have a drain valve, buy one rated for your tank's pressure and have a floor drain or sump pit ready to receive the water.
Installing the check valve and inlet line
Start by shutting off your water source and draining any existing lines. The check valve goes on the incoming water line, right before the tank's inlet port. Wrap the male threads of the check valve with three layers of white thread seal tape, wrapping clockwise so the tape does not unravel when you thread it in. Then coat the threads with pipe dope.
Thread the check valve into the tank's lower inlet port by hand first, then tighten it with two wrenches—one holding the fitting body and one turning the connector nut. Tighten until snug, then give it one more quarter-turn. Do not over-tighten; you will crack the fitting or strip the threads. The arrow on the check valve body should point toward the tank (the direction water flows).
Now connect your incoming water line to the outlet side of the check valve. If you are using copper tubing, solder the connection or use a compression fitting. If you are using PEX or PVC, use the appropriate clamps or fittings for that material. Leave enough slack in the line so the tank can be removed later without cutting pipes.
Connecting the outlet line and pressure gauges
The outlet line connects to the tank's upper outlet port and runs to your home's main water line. Before you connect it directly, install a tee fitting at the outlet port so you can branch off a pressure gauge line. Wrap the tee's threads with tape and pipe dope, then thread it into the upper outlet port using two wrenches, the same way you installed the check valve.
One side of the tee goes to your home's main line. The other side goes to a ball valve, then to a pressure gauge. The gauge lets you see the tank pressure at a glance—when the pump turns on, pressure rises; when you use water, pressure drops. Most systems run between 40 and 60 pounds per square inch, with the pump cutting in (turning on) around 40 and cutting out (turning off) around 60.
Install a second pressure gauge on the inlet side as well, between the check valve and the tank. This gauge shows you the pressure the pump is delivering. If the inlet gauge reads much higher than the outlet gauge, the check valve may be failing. Connect both gauges with 1/4-inch tubing and ball valves so you can remove them for replacement without draining the tank.
Setting the air pressure in the tank
Before you turn the water on, you must set the air pressure inside the tank. The tank contains both air and water—the air acts as a spring that pushes water out to your home when the pump is off. If the air pressure is too low, the tank will not hold enough water; if it is too high, the pump will cycle on and off too often.
The correct air pressure is usually about 2 pounds per square inch below your pump's cut-in pressure. If your pump cuts in at 40 pounds per square inch, set the air valve to 38 pounds per square inch. Use a tire pressure gauge or digital gauge to check the air valve on top of the tank. If the pressure is wrong, add or release air using the valve stem (just like inflating a tire).
You can only check and adjust air pressure when the tank is empty or nearly empty. If the tank is full of water, you will get a false reading. After you set the air pressure, turn the water on slowly and let the tank fill. Watch the outlet pressure gauge—it should rise smoothly as the tank fills.
Connecting the drain valve and securing the tank
The drain valve at the bottom of the tank must connect to a floor drain, sump pit, or outdoor drain so water does not pool underneath. If your tank does not have a drain valve, thread one into the lowest port on the tank using tape and pipe dope. Attach a ball valve to the drain valve so you can shut off the drain when you are not using it.
Run a 3/4-inch or 1-inch line from the drain valve to your floor drain or sump. If you do not have a floor drain, you can run the line outside through a basement wall or window, but make sure it slopes downward so water flows out by gravity. Do not leave the drain line open all the time—water will drain out constantly and the tank will never pressurize. Open the drain only when you need to empty the tank for maintenance.
Once all connections are tight and the drain line is in place, find the tank to the floor or wall with metal straps rated for the tank's weight when full. A 40-gallon tank filled with water weighs about 330 pounds, so use heavy-duty straps and anchor them to solid framing or concrete. This prevents the tank from tipping if a fitting fails or if someone bumps it during maintenance.
Testing the system and checking for leaks
Turn the water on at your source and watch all the connections you just made. Open a faucet in your home to let air out of the lines, then close it. The pump should turn on and pressurize the tank. Watch the outlet pressure gauge—it should rise from the air pressure you set (around 38 pounds per square inch) up to the pump's cut-out pressure (usually 60 pounds per square inch). Once it reaches cut-out, the pump should turn off.
Now open a faucet again and use some water. The pressure should drop as the tank supplies water to your home. When the pressure falls to the pump's cut-in setting (usually 40 pounds per square inch), the pump should turn back on. If the pump cycles on and off more than a few times per minute, the air pressure in the tank is too high or too low—adjust it and test again.
Check every fitting for drips or leaks. If a connection leaks, turn off the water, drain the tank, and tighten the fitting another quarter-turn. If it still leaks, drain the tank completely, unscrew the fitting, wrap the threads with more tape and pipe dope, and reinstall it. Do not ignore leaks—they will get worse and can damage your basement or crawl space.
Common mistakes to avoid during installation
The most common mistake is installing the check valve backward. The arrow on the valve body must point toward the tank. If it points away from the tank, water will flow backward into your source when the pump shuts off, and the tank will not hold pressure.
Another frequent error is forgetting the air valve adjustment. If you skip this step, the tank will not work properly—it will either not hold water or the pump will cycle constantly. Always set the air pressure before you pressurize the tank for the first time.
Do not use galvanized steel fittings inside the tank or on pressure lines. Galvanized fittings corrode quickly when exposed to pressurized water and can clog your lines or fail suddenly. Brass and stainless steel last much longer. Also, do not over-tighten fittings—you will crack them or strip the threads, and then you have a bigger leak to fix.
Finally, do not skip the drain valve or run it to a place where water will pool. A tank that cannot drain will rust from the inside out, and standing water under the tank invites mold and structural damage. If you do not have a floor drain, install one or run the drain line outside.
Frequently Asked Questions
What size tank do I need for my home?
Tank size depends on your household size and water use. A family of four typically needs 40 to 80 gallons. Larger tanks mean the pump runs less often, which extends its life. If you have a well pump, a bigger tank is usually better because it reduces the number of times the pump cycles per day.
Can I install a pressure tank myself or do I need a plumber?
If you are comfortable with basic plumbing and have the right tools, you can install a tank yourself. The work is straightforward—threading fittings, tightening connections, and setting air pressure. If you are unsure about any step, hire a plumber. A bad connection can leak or fail under pressure.
How often should I check the air pressure in the tank?
Check the air pressure once or twice a year, or if you notice the pump cycling more often than usual. Air can leak slowly out of the tank over time, so the pressure may drop. If the air pressure drops below the correct setting, the tank will not hold water properly and the pump will run more often.
What should I do if the pump keeps turning on and off?
Rapid cycling usually means the air pressure in the tank is too low. Drain the tank completely and check the air valve with a tire gauge. If the pressure is below the correct setting, add air. If the air pressure is correct but cycling continues, the check valve may be leaking—water is flowing backward out of the tank when the pump shuts off.
Do I need a pressure gauge on both sides of the tank?
A gauge on the outlet side is essential so you can see when the pump turns on and off. A gauge on the inlet side is helpful for troubleshooting—if it reads much higher than the outlet gauge, the check valve is failing. You can install both or just the outlet gauge if space is tight.