Just finished painting my hallway this weekend and wanted to share a quick hack I learned for getting perfectly clean lines without the paint bleeding under the tape. I used to hate peeling off tape and finding out the paint leaked through anyway.
What you do is, after you put down your painter’s tape along the trim or wall, take a tiny bit of the wall’s base color (the color that is already under the tape) and paint lightly right over the edge of the tape first. Let that dry for a bit, and then go ahead and paint your new color over it like normal.
The base color basically seals the edge of the tape, so if anything leaks underneath, it’s the color that’s already there anyway so you won’t see it. When you peel the tape off at the end, the line is perfectly sharp and clean. Try it next time you’re doing a room, it saves so much time on touch-up work.