Background: I have just finished tiling my shower/tub. Everything has been waterproofed with mapei liquid membrane and fiberglass tape on the seams over cement backer board. The backerboard was installed by a contractor and the holes are a bit bigger than the mixing valve and shower pipe need (but not much). We were using glass tile, so I couldn't use a nice hole cutter to get the CLOSEST possible fit to the edges of these holes or the edges of the fixtures, but all the cuts will be completely hidden by the estucheons/flanges. I used a pipe collar on the copper pipe for the slip on tub spout, but that wouldn't have worked for the shower pipe (needed to be a threaded brass pipe) or the mixing valve (the valve was larger than the only size they seem to make the collars in.
My question is: Do I need to do anything to fill in those smaller gaps between the shower fixtures and the edge of the tile? Do I grout right up to the edge? Do I pre-fill with silicone or kerdifix? Do I just install the flange and estucheon over top?
Thanks in advance.