Best way to secure sink top

[dr_bogenbroom]

This bathroom sink top sits on a cupboard but it’s not secure against the tiles and wall. What would you suggest securing it? I was going to shove a load of Tec 7 in behind it and apply a bead along by the tiles - not sure if this would work?

 

[Exedon]

It's a wash hand basin not a sink.
Assuming it's clean and dry in the gap up to wall squeeze in some CT1 then tidy up seal.

 

[Diver Fred]

Have you looked under the basin towards the back 'cause I'd expect there to be a couple of holes on the back for screw or bolt fixings into the wall.