Before you touch a wrench, be clear about what kind of sink you're working with and what is and isn't changing. A straight swap—same sink type, same hole pattern, same drain location—can be very manageable. The job gets more complex when you change from top-mount to undermount, move from a double bowl to a deep single bowl, relocate the drain, or change the faucet layout from single-hole to 3-hole or 4-hole.
If you're in a stone countertop, undermount work often requires more care and support than people expect. If you're in a laminate top with a drop-in, it's usually more forgiving. Take a few reference photos of the existing plumbing from different angles before you disconnect anything. This isn't about being fancy; it's about knowing how everything was oriented when you go to reassemble it.
A quick code reality check helps you avoid building a leak-prone setup. In the International Residential Code, trap sizes are listed by fixture type: a kitchen sink trap is typically 1 1/2 inches minimum, while a lavatory is typically 1 1/4 inches minimum. That matches what you'll see at the store: most kitchen tubular P-trap kits are 1 1/2 inch, and bathroom sink drain parts often start at 1 1/4 inch.
If your wall stub-out is one size and your tailpiece is another, don't panic—reducers and washers are common, but you want the right ones, tightened correctly, with the washers seated straight. Keep a few spare slip-joint washers on hand; they're cheap insurance against a torn washer that ruins your momentum.
Clear out the cabinet so you can move freely and see what you're doing. Put a bucket under the trap, lay down a towel, and consider improving your task lighting. Something as simple as LED ceiling light fixtures recessed above the sink area can make it easier to spot a cross-threaded nut or a washer that's pinched.
