Your pre-plumbed loop has shutoff valves built in (if you’re lucky—check!). Turn those valves to “OFF,” then unscrew the brass caps. Wrap Teflon tape clockwise around the threads of the softener’s inlet and outlet ports. Most machines come with flexible hoses—connect the IN port to the IN pipe, and the OUT port to the OUT pipe. Tighten with your wrench until snug, but don’t Hulk it; too much torque will crack the brass.
If you have copper pipes without valves, you’ll need to cut a section out and install “compression unions.” It sounds scary, but it’s just like screwing on a fancy Lego piece. Surprise fact: The same compression fitting technology is used on NASA’s space station toilets. If it works in zero gravity, it’ll work in your crawlspace.
