Begin by preparing your work area. Clear any items from the tub deck and place towels or rags on the floor around the access panel to catch any residual water. The most critical action in this step is to shut off the water supply to the faucet. Locate the main water shut-off valve for your house (often in the basement, a utility closet, or near the water heater) and turn it fully clockwise until it stops. Return to the garden tub and open both the hot and cold handles of the old faucet to drain any remaining water from the lines and relieve pressure.

With the water off, you must now access the faucet's plumbing. Locate the access panel on the wall of the tub surround or an adjacent wall. These panels may be held in place by screws, clips, or simply pressure-fit. If screwed in, use the appropriate screwdriver to remove the screws. Carefully pry the panel open and set it aside. Use your headlamp to inspect the plumbing, familiarizing yourself with the hot and cold supply lines, the valve bodies, and the connections leading to the spout.

Place a bucket and some rags directly beneath the faucet's water connections to catch any trapped water. Using an adjustable wrench, grip the coupling nut on the flexible supply line that connects to the hot water valve inlet. Turn the nut counter-clockwise to loosen and disconnect it. Repeat the exact same process for the cold water supply line. Expect a small amount of water to drain out.

This is often the most challenging step. First, disconnect the flexible hoses that run between the hot/cold valves and the central spout tee. These are usually hand-tightened or require pliers. Next, use a basin wrench to reach up behind the tub deck to the large mounting nuts that secure the faucet handles and spout to the deck. The basin wrench is designed for this tight space. Latch its jaws onto a nut and turn counter-clockwise to loosen. It will take several turns. Once all three mounting nuts are removed, have a helper lift the old spout and handles from the top of the tub deck.

After removing the old faucet, the tub deck will likely have residue from old plumber's putty or sealant. Use a plastic putty knife to gently scrape away all of this old material. Be careful not to scratch the surface of the tub deck. Once the bulk of the material is removed, use a rag with an all-purpose cleaner or mineral spirits to wipe the surface completely clean. A clean, smooth surface is essential for creating a watertight seal with the new faucet.

Unpack your new faucet and review the manufacturer's instructions, as assembly can vary. Typically, you will first install the valve bodies. From underneath the deck, feed the threaded shanks of the hot and cold valve bodies up through the handle holes. From the top, place any included gaskets or seals and thread on the decorative handle bodies. From below, thread on the mounting washers and nuts. Hand-tighten them first, then use the basin wrench for a final quarter-turn to secure them. Next, apply a bead of plumber's putty or silicone sealant (check instructions) to the underside of the new spout's base. Insert the spout into its deck hole, and secure it from below with its mounting hardware. Finally, connect the flexible hoses from the valve bodies to the spout's tee fitting.

Now, reconnect the main water supply. First, wrap the male threads on the new hot and cold valve inlets with Teflon tape. Wrap the tape 3-4 times in a clockwise direction (the same direction you will tighten the nut). Align the flexible braided hot water supply line with the hot valve inlet and thread the coupling nut on by hand until it's snug. Then, using two adjustable wrenches—one to hold the faucet valve body steady and one to turn the nut—give it a final quarter to half turn. This two-wrench technique prevents stress on the new faucet. Repeat the entire process for the cold water supply line.

This is the moment of truth. Go back to your main water shut-off valve. Turn it on SLOWLY, only about a quarter turn at first. This allows the pipes to fill with water under less pressure, reducing the shock to the system. Immediately return to the access panel with your headlamp and dry paper towels. Meticulously inspect every connection you made: where the supply lines connect to the valves, and where the valves connect to the spout. Wipe each connection with a dry paper towel to easily spot any moisture. If all is dry, go back and open the main valve all the way. Check for leaks again.

With the water on and no leaks detected from below, it's time to test the faucet's operation. Turn the hot water handle and let the water run for a minute to purge any air from the line. Check that the water flows smoothly from the spout. Turn it off and repeat with the cold water handle. Then, turn on both to check the mixed flow. While the water is running, perform one final leak check at the access panel. Once you are confident everything is working correctly and is completely dry, you can clean up your tools, wipe down the tub deck, and reinstall the access panel.