You can try to seal your mouth tightly, then put it in the sun, or pour boiling water into it. According to the principle of thermal expansion and cold contraction, gas expands to support the deformed part.

Barreled bucket:

Barrel barrel refers to pure barrel, which mainly includes "pet drinking water barrel, PC barrel and miscellaneous barrel". The most common in the market is the sundry bucket (all kinds of recycled waste plastics, which may contain dirty PC materials and become thermoplastic twice or even many times, toxic and carcinogenic); PET barrel is mainly used in supermarkets, and it is a disposable packaging container like ordinary beverage bottles. The State Bureau of Quality Supervision does not allow reuse of water. Nowadays, there are fewer and fewer real PC barrels, which are the most environmentally friendly and economical ideal canned containers for drinking pure water.