prova così...

$query2=("select distinct pockets.pocket_type, pockets.pocket from (pockets join (dispensers join (collocations join (locations join circuits on circuits.circuit = locations.location_circuit) on locations.location = collocations.collocation_location) on collocations.collocation_dispenser = dispensers.dispenser) on dispensers.dispenser = pockets.pocket_dispenser) where circuits.circuit=".$circuit);