Some advice/comment please.
I have just fitted a wall mounted basin of "unbranded/unknown brand - from
Homebase" and concerns started to arise when fitting the Grohe waste - when
central inside the basin the waste "tube" was against the edge of the of
the hole on the underside. Having fitted the basin it was noted that the
basin didn't fully drain leaving a crescent shaped pool approx 2mm deep 40mm
"front to back" , looking down onto the basin running from 4 to 8 o'clock
and about 10mm from the waste at 6 o'clock increasing to 20-30mm at the
"ends". Having an identical basin for the second bathroom I've been playing
with a marble and a spirit level on the back (wall mounting) face and found
that unless the back face is tipped back (i.e. by raising the front edge)
2-3mm in 180mm (height at back) then a marble placed at "6 o'clock" will
remain in the basin. Therefore for this basin to drain it needs to mounted
on a wall that is around 30mm out of true over 2.4m. There is no flat plane
on the top of the basin to use as a reference.

Is this sort of scenario normal and should I be inserting packing at the
back of the basin to get complete drainage?

Guidance on fixing would be appreciated. I've currently fixed the basin to
the wall (M10 studs) with a piece of 3/8" plasterboard as "packing"
(awaiting tiles) and intended to remove the basin, tile the whole wall and
then fix the basin on a bed of silicon sealant. Is this the correct
procedure or should I be tiling round the basin.

Thanks
Pete