There is a toilet on the Hongqiao plane

Some but the toilet is smaller, the toilet is relatively narrow, the domestic flight time is generally shorter, go to the toilet in advance before getting on the plane, and basically do not need to go on the way. International flights are long, and you should be aware that you cannot use the toilet when the plane encounters turbulence and take-off and landing.

There are fixed storage tanks that will not be dumped at will >>>More

The toilets on the plane certainly have smoke detectors.

a piece in the ceiling. >>>More

Alarms are installed on the ceiling of the restroom and are used by the smoke detection system to detect the presence of smoke in the aircraft cabin that is a sign of fire, allowing the pilot to take timely action against the fire.

Generally speaking, the passenger plane is sucked into the storage box connected to the toilet through a vacuum, and then pumped away by the ground staff with a special vehicle after landing, and then transported to a unified storage point in the airport, where it is towed to the domestic sewage treatment plant by sanitation workers every day for treatment.