Connecting PEX to copper is a common thing to do when adding new supply lines to an existing home. Sweat adapters make this transition simple. Female sweat adapters come in many varieties for different kinds of PEX fitting systems (check out the article “Connecting PEX Plumbing” for a rundown of the major PEX fitting systems ). These adapters are soldered—or “sweated”—onto the copper tubing, allowing for a solid connection between the copper and the PEX. Here we’ll use an adapter designed to transition from copper to a PEX crimp connection. Start by cleaning the outside of the copper tubing with plumber’s cloth, and the inside of the fitting with a wire brush. Then, use an acid brush to apply tinning flux to both the outside of the copper and the inside of the fitting. Then slip the fitting onto the tubing with a slight twist, making sure it’s fully seated. Unroll about 6 in to 8 in. of lead-free silver solder and bend it at 90° about 2 in. from the end to make it easier to solder around the joint. For 1/2-in. tubing, you’ll only use about 1/2 in. of solder per joint. Heat the fitting at the connection with a torch, keeping the tip of the brightest part of the flame in contact w...