Studbuddy

Secure the vanity to the wall, then caulk the joint with Mapesil-T silicone that is as closely matched to the color you want. For a super neat and clean caulk joint, tape off both the wall and the counter, masking off just the area that you want the caulk to go. Caulk the joint and wipe off all excess caulk leaving the edge of the tape near the joint with little or no caulk covering it. Then pull the tape off, revealing a nice cut line. Lastly, use super-soapy water and a finger to smooth out the joint. You have to do this quickly with no time to waste once caulk is applied, or it will be a disaster.

THIS IS THE WAY. I paint professionally. We tape all trim except the tops and bottoms of windows/ doors where you cant see. We then use white or clear AlexFlex caulk and lay down the thinnest bead possible on the edge of the tape. Then, wipe off most of the caulk or spread it out as thinly as possible. Paint the masked area immediately, and remove the tape immediately after painting to reveal a crisp cut line with no bleeding.