Seat for one lad showing bottle (6)
I believe the answer is:
carboy
'bottle' is the definition.
(I've seen this before)
'seat for one lad' is the wordplay.
'seat' becomes 'car' (car seat is a kind of seat).
'for' is a charade indicator (letters next to each other).
'one lad' becomes 'boy' (I've seen this before**).
'car'+'boy'='CARBOY'
'showing' is the link.
(Other definitions for carboy that I've seen before include "Large bottle to contain chemicals - boa cry (anag)" , "Large bottle encased in wicker" , "Large round bottle surrounded by framework" , "Large cushioned container for liquids" , "Large bottle for corrosive liquid" .)