Pentair 1.0 Service Manual page 7

Special Attention for situations where a Filter and a Softener are installed
together:
When a whole house filter and a softener are installed side by side, the preferred approach is to run a
separate drain line from each unit all the way to the point of termination. If this is not done, there is
the potential for drain water from the filter to back feed through the softener and overfill the brine
tank, especially when drain lines are run overhead. (Please note that back feed goes only into the
brine tank, not the service line.)
If circumstances require you to tie the drain lines together, please use one of the following methods
to avoid back feed issues:
Option 1: Run the drain lines from both systems to the point of termination, and tee them together
before the air gap. (See figures below)
FILTER
Option 2: Install a PVC check valve with a light spring on the Softener side to prevent back flow to
the Softener. (See figure below)
2 SEPARATE DRAIN LINES
SOFTENER
TREATED
WATER OUT
FILTER
SOFTENER
TREATED
WATER OUT
2 SEPARATE
DRAIN LINES
TEE
APPROVED FLOOR DRAIN
SPRING CHECK ON DRAIN
LINE AFTER SOFTENER
AIR GAP
7