Remove the fixture, if possible. Hold a tile to one side of the pipe and mark the top and bottom edges of the pipe's diameter on the tile. Even if the fixture has not been removed, use this technique to measure where the hole will fall (Image 1).
Hold the tile below the pipe, in line with its column of full tiles, and mark on it the left and right edges of the pipe's diameter (Image 2).
Use a try square to join the marks, forming a square where the tile will fit over the pipe. Join opposite corners to find the center (Image 3).
Adjust a tile hole cutter to the size setting you need (Image 4).
Attach the hole cutter to a drill, set its point on the mark in the center of the square guide lines, and remove a circle of tile (Image 5).
Apply tile adhesive directly to the tile, and put the tile in position over the pipe. If it has not been possible to remove the fixture, score and snap the tile along a line through the hole, so that you can fit the tile around the pipe (Image 6).