A $180 \mathrm{~cm}$ high, horizontally based, cylindrical fuel tank is equipped with a tap at the bottom and a filling nozzle at the top. The latter can fill the tank in 1 hour. If we open both the filling nozzle and the tap for 5 minutes, the fuel level in the tank rises by $10 \mathrm{~cm}$. How long will it take to empty a full tank through the tap?