drilling holes in tiles

What's a box cutter? I thought that's what americans called Stanley knives?

You could use a diamond hole cutter,expensive but accurate.There are plenty of adjustable tile hole cutters available from tile suppliers around £5 -

When I did this in my bathroom, I put the tile on a block of wood, and masking tape over where I wanted to drill and use a masonary bit on a normal drill (not on hammer action)

you may want to start the hole off by cutting a small amount of the glaze away in the centre of the hole with a small tile scorer to prevent the drill skidding across the tile surface.

Drill from the glazed side into the tile as you do get some breakthrough damage on the other side.

Worked for me on very cheap tiles...

Scott

If it is the type of valve that has metal cone shrouds that cover where the pipes exit the wall, then you don't have to worry about making a perfect hole. So you can mark where you want the hole and then drill a sequence of small holes round the annulus of the bigger hole. Finally knock out the centre section.

I cut the tiles in half on a section through the point where the pipes needed to go through, then cut square holes with an angle grinder, then covered them with the cone shrouds as mentioned. Looks fine.