What we recommend is drilling a 30mm hole into the tile and taking out a plug. Take out the plasterboard if you need to as well.
This photo shows the hole options from the bathroom fitters kit. At 16mm its too pokey. Get the 30mm core out.
Once you have the holes drilled out then look beyond the plasterboard to find a solid substrate like brick or wood. If its just a stud wall then I would go into the room behind, remove the plasterboard and provide a substantial bracket or brace at the back of the sink. Its cheaper to cut out plasterboard in the room behind than take of the tiles.
Oh and if its masonary then you will be able to drill through the 30mm hole without fear of smashing the tile on the wall. If you went for the 16mm then its too close.
A fisher fixing kit pushed through a 16mm hole is too risky.
Pop it through a 30mm and you will get the best view of the substrate behind to ensure a solid anchor
The bathroom Fitters Kit contains both 16mm and 30mm
Note Professional Builder recommend our 16mm when things are easier...
So I would use the 16mm when you know whats behind the wall.
Failing that you could drill out with a 16mm first and then if you need to open out the hole use the 30mm.
Just a thought