6mm for drill bit.
Normally use for bathroom fixture or etc. Anchor that usually sell as RM1 per strip.

The anchor package don't have the information?

Where you get a drill without the size? Most of the drill bit have the size on the shaft. (Drill lock side)

If those thing don't have any information, don't buy. You not experience to look for such non information parts. Go to hardware shop to get. At least the guy can pick the right part for you.

You got to see the basin, toilet bow inlet the pipe height to know where the pipe run. It is hard to explain for me. 

Take a picture of your bathroom and post here. I try to check it out.

The drill size is not the problem. Just choose the size slightly smaller than the screw you wanted to use. The more important thing is to use suitable drill bit. For masonry, brick concrete; 1 type, For wood another type, steel has low and high speed type. The one that many contractor failed to use is the proper drill bit for tile. That is why most of you see chipped and cracked tile. 

Your toilet piping is using PVC pipe. So you can't hear anything beside your drill sound.

If you see the stopcock on top, that is the main pipe from the tank.

http://www.lazada.com.my/catalog/?q=bosch+multipurpose

multipurpose doesn't cost that much but it cannot be used to drill quartz top, I believe you need diamond coated tip for that one.

Tile doesn't really need 30minutes to drill, just keep dipping the bit into the water to keep it cool while drilling, i'll say I used 5 minutes average per tile hole, I was only using 650w b&d impact drill, my friend used his bosch rotary hammer drill and he drill a tile hole are pretty much under few seconds.