Begin to scrape away at the old caulk using your tool. Be careful not to scrape the sink's porcelain or surrounding surface. If you find the caulk is too hard and not budging, you can heat it with a hair drier, then scrape it while it's softened.
Jane Tip: Removing the old caulk is vital to the success of this job. Make sure you do so thoroughly, otherwise your new caulk won't adhere correctly.
After the old caulk has been removed, clean the area well with soap and water. Scrub away any lingering caulk. Using a mixture of 3 parts water to 1 part bleach (and wearing your latex or rubber gloves!), dab the surface where the grout was removed. This will kill any mold.
Let the surface air dry for as long as possible, up to 24 hours. The caulk needs a clear, dry are to adhere best.
When you go to open the new tube of caulk, cut the end at an angle and don't cut too far up the tube. You'll have extra-large beads of caulk to deal with if the hole is too big. It's better to keep cutting if the hole is too small for the caulk to flow evenly. We aim for a hole about three-eighths of an inch for most jobs.
With a steady hand, squeeze a thin bead of caulk on the seam where the sink meets the surrounding countertop.
Smooth out any bumps using your finger.
Jane Tip: If you are using silicone caulk, dip your finger in alcohol first. For latex, use water. (If you are allergic to latex, wear protective gloves)
It is best to leave the caulk to dry for another 24 hours.
That's it! Your sink is now re-caulked, sanitized and ready for years of use. You've saved yourself yet another handyman bill and helped prevent mold from building up in your walls. Congratulations!