There was a smell of petrol in the toilet and we were on the ground floor

Caused by sewer odor.

Sewer is a kind of urban public facility, which refers to the pipe of the building that discharges sewage and rainwater; It also refers to the underground passage of a city, factory or village to drain sewage and rainwater.

Sewers are a type of urban public facility that has been used as early as the ancient Roman period. They picked up some waste from the garbage dump and built a simple "house" to live in, with beds, wardrobes, bookcases, etc.

The Idalalians later left the Romans with the most magnificent sewers in the ancient world: the Cloaca Maxima. Around the 6th century B.C.E., The Idalarians dug the sewers that drained into the Tiber River, the main channel of which was more than 16 feet wide, and was later expanded by the Romans.

The 7 branches of the sewer flow through the city streets and eventually flow into the main road, the Maxim sewer.

The sewer is full of water, press down with a leather plug, and then lift it violently, so that a certain pressure and pumping force will be formed, and the blocked debris may be washed away; But if the plug is too dead, I'm afraid only the serpentine pipe will do, you can also use the wire mentioned above, but this is expensive and difficult to get, it is best to find someone to dredge, and there is also a thing called pipe dredging agent, which is sold in supermarkets, you can also try.

It may be because of the long-term accumulation of odors in the sewer, which may be mixed with gasoline, which should be taken seriously, do not smoke in the toilet, especially not thrown into the sewer, which is very dangerous...

You should test whether it will cause an explosion.