Yeah the bar section has to be sealed all the time or all the water above it would drain out. The only way to clean that part would be to drain the main tank to below the bottom of the connection, drain all the water out of the little bridge thing until there was only water in the flat bar part, and then remove the top if there was some way to do that.
Seems awful risky though. I could see maybe the bar and connector being fake and actually separate from the main tank, but the tank having fish in it. Basically it could be a tank with a fake extension to make it look cool for the bar.