Install
Setting Up a Water Softener Drain Line
A water softener drain line is the 1/2-inch tubing that carries backwash and rinse water from the control valve to a drain; it must be sized for its length, kept within the manual's lift limit and end above the drain with an air gap.
On this page
Quick answer
- Use 1/2-inch inside diameter tubing at minimum.
- Fleck: go to 3/4-inch over 20 feet or 7 gpm backwash.
- Pentair allows up to 6 feet of lift; SoftPro Elite allows 3 feet.
- End the tube above the drain; never push it into the pipe.
- The brine tank overflow needs its own separate line.
What the drain line carries
During regeneration the control valve sends several kinds of water down the drain line. Backwash flushes the resin bed in reverse to loosen sediment. Brine draw and slow rinse push the salty brine through the resin and out, carrying the hardness the resin picked up. Rapid rinse then flushes the leftover brine so the house gets soft water, not salty water. On a Fleck 5600SXT that order is backwash, brine draw and slow rinse, rapid rinse, then brine tank fill; our regeneration guide explains each step.
That adds up to a fair amount of water. Penn State Extension puts it at about 50 gallons per regeneration. The flow rate during backwash matters for sizing the line; Pentair's 5600SXT backwash rates climb with tank size, from 2.0 gpm on the 1.0 cubic foot model up to 3.5 gpm on the 2.0 cubic foot model.
Every drain port also has a small part that sets that flow: the drain line flow control (DLFC). If it plugs, the valve cannot regenerate properly. The Fleck manual links a plugged DLFC to two common faults, a brine tank full of water and a softener that fails to draw brine.
Size, length and height
Diameter. The Fleck 5600SXT manual sets a 1/2-inch minimum for residential drain lines and moves to 3/4-inch when backwash flow is over 7 gpm or the line is longer than 20 feet. SoftPro's Elite guide also uses 1/2-inch ID vinyl tubing on the drain port.
Distance and lift. Drain lines can run uphill to reach a drain, but only so far, because the valve has to push the water up. The numbers depend on the valve:
| Source | Limit |
|---|---|
| Fleck 5600SXT manual | 1/2-inch minimum; 3/4-inch over 20 ft or over 7 gpm backwash |
| Pentair 5600SXT manual | Unit above the drain and no more than 20 ft from it |
| Pentair 5600SXT manual | Lift up to 6 ft if the run is 15 ft or less and pressure is at least 40 psi |
| Pentair 5600SXT manual | Add 2 ft of lift for each extra 10 psi |
| SoftPro Elite guide | Maximum 3 ft above the drain port; contact SoftPro if higher |
Follow the manual for your own valve. If your drain is further or higher than it allows, you may need a closer drain point, a larger line, or a plumber's help.
Siphon protection. When an elevated line comes back down to a drain that sits below the valve, Pentair says to form a 7-inch loop at the far end, with the bottom of the loop level with the drain connection. Where the line empties into an overhead sewer pipe, it calls for a sink-type trap instead.
Where it can drain
SoftPro's Elite guide lists the accepted drain points: an existing softener drain, a floor drain, a laundry tub or sink, a washing-machine standpipe, or a sewer pipe, provided it has a trap, a riser and an air gap on top.
Whatever you choose, the tubing must stop above the drain. All three install documents (Pentair, Quality Water Treatment and SoftPro) forbid sliding the tubing down into the drain, the sewer pipe or the trap. The open space they require above the drain is twice the tubing diameter, and never under 1 inch. The air gap guide covers fittings and code. Local plumbing code has the final say on where the line may end; if you are unsure, ask a licensed plumber.
On a septic system, think about where the discharge goes; the views differ, and our page on softeners and septic systems sets them out.
Securing the line
A drain line that pops off or flips out of the drain during a 2 a.m. backwash floods the floor, so fasten both ends.
- At the valve. Push the tubing onto the drain port barb and tighten a hose clamp over it. On a SoftPro Elite, leave the barb in place because it holds the required flow restrictor.
- Threads and solder. The Fleck manual allows only Teflon tape as a sealant on the drain fitting, and asks for at least 6 inches between the DLFC and any solder joint so heat does not damage it.
- Along the run. Keep the tubing free of kinks and sags; a kinked line restricts flow the same way a plugged DLFC does.
- At the drain. Fix the end above the drain so it cannot drop into the pipe or jump out, keeping the air gap.
- Overflow line. The brine tank overflow is a second, separate 1/2-inch tube in Pentair's manual. Keep it below the overflow elbow all the way down, give it its own air gap, and do not join it to the valve's drain tubing.
Once it is all connected, the Fleck manual says to check the drain seal for leaks with the control in Backwash. If you find resin beads at the drain end, the Fleck manual points to air in the water system or a wrong-size DLFC; see resin beads in the water.
Common questions
Can the drain line share a standpipe with the washing machine?
SoftPro's Elite guide lists a washing-machine drain as an accepted drain point. Keep the tubing end above the standpipe with an air gap, and follow local code.
Is 3/8-inch tubing big enough for a softener drain?
The Fleck and Pentair manuals set 1/2-inch as the minimum, and the Fleck manual calls for 3/4-inch on long runs or high backwash flow. Use at least 1/2-inch on a Fleck valve.
Why does water run down the drain line constantly?
In the Fleck manual's table, nonstop drain flow comes from one of three faults: the valve failing to reach its programmed position, dirt lodged inside the control, or a leak inside the valve. Start with the troubleshooting guide.
Can the drain line run up to a ceiling sewer pipe?
Within limits. Pentair allows up to 6 feet of lift with a short run and at least 40 psi, and calls for a sink-type trap where the line empties into an overhead sewer. SoftPro's Elite guide caps lift at 3 feet.
Related guides
More help: see our water softener guides.