A softener sends its rinse and brine water down a drain line on every regeneration. The line is short, but it is where leaks, backflow, and overflow start. Walk through the steps below before you accept the install as finished.
Confirm the drain point before the work starts
Find the drain point you will use, whether a standpipe, a floor drain, or a utility sink with an approved receptacle. Read the installation manual for the maximum height the drain can rise above the valve and the longest run it allows. Check your local plumbing code for the air gap or receptacle requirements, since local rules decide what the inspector expects.
Install the drain tubing
Cut the tubing square and clean. Route it without sharp bends or kinks, because a kink restricts flow and can make a regeneration run long. Support the tubing so it does not sag or rub against the wall. Keep the end clear of the drain water so it cannot siphon back into the valve, and leave the air gap or the receptacle gap the code requires.
If you are not comfortable cutting, fitting, or sealing the connections, have a licensed plumber make the final connection. Ask them to show you the air gap or receptacle before they leave.
Test the flush before you accept the job
Put the softener through a manual regeneration with a person standing by the drain. Watch the water come out of the end of the line. Check each fitting for drips, and look for any water rising back up the line or pooling near the valve. Let the cycle finish, then return to the drain an hour later and check again. A leak that appears after the first hour is still a leak.
What to ask the installer
Ask the installer to show you the drain route, the height, and the air gap or receptacle. Ask what to do if the drain backs up during a regeneration, and who to call. Get the answers written on the job paperwork. A clear answer now saves a dispute about which part of the drain belongs to whom.