Secure the sink in position with a piece of lumber and a bar clamp. Cut a section of 2 in × 4 in (5.1 cm × 10.2 cm) lumber so it’s at least a few inches/centimeters longer than the width of the opening for the sink in the countertop. Lay this piece of wood across the opening. Then, while a second person lifts the new sink up into place from beneath, feed the bar clamp up through the drain opening of the sink so that one of its clamps holds up the sink from below. Secure the other clamp to the piece of wood and tighten it.
Make sure the clamp is tight enough to make the some of the silicone caulk squeeze out between the rim of the sink and the underside of the counter. Wipe away this excess caulk with a damp rag. Secure the included clips in place with screws or epoxy. Your new undermount sink will come with support clips to place around the underside of the sink where it meets the underside of the counter. In some cases, these clips may attach with screws. If so, drill pilot holes and use a screwdriver to secure the clips in place. Otherwise, use the brand or type of epoxy recommended by the sink manufacturer.
In most cases, the clips are adhered in place with a 2-part epoxy that hardens in about 10 minutes after being combined. Follow the product instructions carefully and apply the proper amount to each clip. Then press them into place as per the installation instructions for your sink.
Wait 24 hours, then install the drain. Even though the epoxy should be fully set in 10 minutes, it’s important to give the silicone adhesive time to cure fully. Leave the piece of lumber and bar clamp in place for a day before removing them. After that, you can put the drain in place and continue with the installation.
Like faucets, drain installations vary by type and brand, but the process is DIY-friendly if you follow the instructions carefully. You could rely on the epoxy to hold everything in place after 10 minutes and not wait the full 24 hours before proceeding, but this is not recommended. Be patient.