For four months, a group of Zhenghua Secondary School students would stay back after class for an hour twice a week.
They were not attending remedial classes or co-curricular activities, but washing dirty PET bottles they had collected from every classroom in the school.
Thanks to the dedication of these students who call themselves the "eco-champions" - and the support from the rest of the school - Zhenghua Secondary emerged champion in an inter-school recycling contest that saw 45 participating primary and secondary schools.
Organised by the Singapore Environment Council (SEC) in partnership with Sembcorp Industries, the One Less Plastic - PET Bottle Collection Contest was held from November last year to February. It was sponsored by Coca-Cola.
The contest aimed to educate students on the types of plastic that can be recycled and how to do so.
An SEC study in 2018 found that Singaporeans used about one to three PET bottles a week.
The study discovered a lack of awareness among students on the types of plastic that can be recycled and how to recycle them, said Ms Tay Sok Leng, head of business strategy and development at the SEC.
For the contest, a 660-litre recycling bin was placed in each participating school and Sembcorp's ezi mobile app was used to track the weight of the recyclables collected.
Each school's total score was based on the collected bottles' weight in relation to the school population. A 10 per cent penalty would be deducted from the score if contaminants such as food or liquid waste were found in the bin. Contamination would make the entire collection unsuitable for recycling.
During the contest, Zhenghua students put up posters around the school to encourage everyone to recycle. They also collected PET bottles from waste bins in the classrooms to wash and dry them.
"If we saw a spot of hardened liquid or parts of the bottle which still had remnants of the liquid, we would wash them again," said Secondary 2 student Beatrix Han, 14, who was part of the core team of student volunteers for the contest.
The teaching staff also chipped in.
"One of our teachers led by example by bringing used bottles from home to the school to be recycled. Another teacher dirtied her hands by picking up bottles from a big trash bin to demonstrate to us that this would be a project that needs perseverance," said Secondary 2 student Javier Chua, 14.
The school collected a total of 67kg of recyclable PET bottles and bagged the first prize.
A group of students will go on a learning trip to Malaysia later this year, sponsored by Coca-Cola. They will visit the brand's bottling plant in Kuala Lumpur and explore Pulau Ketam, an island off the coast of Port Klang in Selangor, which is vulnerable to marine debris.
SEC's Ms Tay hopes the students will continue with good recycling habits and encourage people they know to recycle PET bottles the right way: rinse, dry and recycle.
Javier is one example. He used to buy bottled water, but now he takes along his own reusable water bottle. Additionally, he makes it a point to pick up PET bottles whenever he sees one. "I also ensure that every PET bottle I see is recycled, no matter how dirty it is," he said.