Just finished my first trim around a plumbing fixture and it worked out

I did the same framing method in my laundry room last spring and yeah, the measuring is the killer part. I must have cut that left-hand miter four times before the piece sat right against the pipe. What saved me was cutting the piece long and sneaking up on it with a block plane instead of going back to the saw every time. A couple light passes and the trim just kisses the escutcheon.

One trick my father-in-law showed me: hold the piece in place and trace around the pipe with a pencil, then check the line with a square before you cut. Sounds obvious but I was eyeballing it for the first two attempts and that's where all my gaps came from. I'll say though, on the sink side of the same room I just notched the bottom of the board out with a jigsaw and let the escutcheon ring cover the rough edge, and a year later I honestly can't tell the difference unless I'm down on the floor looking for it. So for anybody reading this who doesn't want to spend a whole afternoon on miters, the notch route holds up fine too.

Also a dab of painter's caulk where the trim meets the escutcheon hides any hairline gap. It's removable if the valve ever needs swapping, wich is the one thing I'd worry about with glue or anything heavier.

I gave up on framing around pipes years ago and just notch the board instead. Did our main floor bathroom with some cheap oak stock and cut a U-shaped notch out of the back edge with a jigsaw, sized so the escutcheon ring covers the whole cut. Once that flange is screwed to the wall you honestly cannot see where the trim was relieved. Took me ten minutes versus the hour I once spent fussing with compound miters around a supply line under the kitchen sink.

The trick is making the notch slightly smaller than you think you need and test fitting against the pipe before it goes on the wall. If the trim rocks at all, shave a little more out. A rattan file or even a half round rasp cleans up the jigsaw marks fine, and paint grade trim hides everything anyway. I know some folks feel the notched board is weaker at that spot, but with a decent bead of construction adhesive behind it and the baseboard nailed to the studs on either side, it has never moved on me. My hallway run has taken vacuum cleaner hits for six years now with no sign of splitting at the pipe. Maybe it depends on the trim profile though. With a tall profile like colonial or anything with a big cove, I could see the framed look earning its keep. On flat stock I would not bother again.

Been doing trim since the days when half the houses around here had no escutcheons at all, just bare pipe coming thru plaster, and we'd scribe the board with a compass and cut it with a coping saw. Same idea works today. Set the board in position, scribe the pipe profile, and nibble out the waste slow. Takes longer to explain than to do.

One thing I learned the hard way: dry-fit the valve side before you nail anything else down. Pipe work is never plumb, and a trim piece that fits at the bottom will bind at the top every time. Check it with the board loose and you save yourself a pull-and-recut.

Reading this as someone who just put flat trim boards in my hallway and honestly just cut a big messy hole and shoved the pipe through it. There's a gap maybe the width of a pencil all around and it bugs me every time I walk past. Sounds like the ring thing that screws over the pipe might hide that? Also wondering if my board will even work for the frame-around method since it has zero thickness to it, it's just flat.