While an adjustable wrench can handle some tasks, a basin wrench (like the TEKTON WRN92004) is highly recommended. Its specialized design allows you to easily reach and tighten nuts in the tight, awkward space under the sink, making the process much smoother and preventing frustration, especially for beginners.

If your shut-off valves are stuck or leaking, do not force them, as this could cause a more significant leak. You might need to turn off the main water supply to your house to prevent flooding. This usually indicates that your shut-off valves need replacement, which is a separate project best addressed before installing a new faucet.

Leaks commonly occur if the supply line connections or mounting nuts aren't sufficiently tight. First, gently but firmly tighten all supply line nuts and mounting nuts under the sink with your wrenches, being careful not to overtighten and strip threads. If the leak persists, turn off the water, disassemble the connections, ensure all washers and O-rings are correctly seated, and reapply plumber's putty if applicable before re-tightening.

Plumber's putty (like Oatey 311662) is the traditional choice for sealing the faucet base against the sink, creating a watertight seal that allows for easier removal in the future. Silicone caulk can also be used but creates a more permanent bond, making future faucet removal more challenging. Always check your new faucet's manufacturer instructions, as they may specify a preferred sealant or prohibit putty for certain sink materials.