In extreme sub-zero winter conditions, why must a bus driver regularly drain moisture from the pneumatic air brake reservoir tanks (储气筒放水)?

1. Condensed water in air tanks can freeze into ice inside pneumatic brake valves, air pipes, and relay valves, causing complete air brake failure
2. Water accumulation increases the bus's curb weight by over 5 metric tons
3. Water in air tanks causes the bus alternator to short-circuit through the tires
4. Air tanks must be drained so they can be filled with liquid anti-freeze oil daily