Re: Building a custom vanity
My guess is that at the very least they'd be pocket screwed together (commercial production assembly ). If this was a custom built unit then it was either biscuit joined or mortise and tenoned. For this application I'd recommend biscuit or pocket screws for ease. Because this is a vanity which should also be secured to the wall, it doesn't need to be as strongly built as a stand alone table would be.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!