"I know I can sell my garbage here so I keep it," said the 60-year-old, who like many Indonesians goes by one name. "I used to throw everything onto the street but I have started telling myself that actually the garbage is useful."
Mahmud, who suffers from arthritis, is one of many members of the Klinik Bumi Ayu in Malang who regularly bring in rubbish in exchange for check-ups and medicine.
There are five such centres in the city that are part of a scheme dubbed "Garbage Clinical Insurance" by its 24-year-old founder Gamal Albinsaid, offering treatment and advice for free to some of the country's poorest.
As Southeast Asia's biggest economy struggles to spread the riches earned in recent years to the poorest in society, the clinics are a creative attempt to fill the gaps left by a threadbare welfare system.
The government this year began rolling out what is supposed to be a universal healthcare system across the sprawling archipelago of 250 million people.
Once fully implemented by 2019, it is expected to cost around $15 billion a year -- but critics say it is underfunded and Indonesia lacks enough well-trained medical staff.
In a country where half the population lives on $2 a day, spreading the gains from a sustained economic boom has been in sharp focus recently, with contenders running in July presidential elections pledging to better the lot of society's underprivileged.
Beyond healthcare, Albinsaid's initiative has had another notable benefit -- it has created an army of cleaners to clear the streets in and around Malang, which like many cities in fast-growing Indonesia struggles to keep litter from piling up.
Albinsaid decided to open a first centre in 2010 after hearing the story of a young daughter of a rubbish collector who died after contracting diarrhoea. Her family could not afford treatment.
That clinic failed to get off the ground, but in 2013, Albinsaid and four others got together the funding to open five centres in Malang, and they have so far been doing well.
His achievements were recognised in January when he was awarded the Unilever Young Sustainability Entrepreneur Prize by Britain's Prince Charles at a ceremony in London, which included 50,000 euros ($70,000) in financial support and mentoring.
- Trash for treatment -
People who want treatment at the clinics bring in rubbish once a week on Saturdays. They must collect 10,000 rupiah (90 US cents) worth of garbage every month to be a member of the scheme, and this qualifies them for two visits a month.
Different types of rubbish are worth different amounts, according to Albinsaid. Organic waste can be turned in to fertiliser which is sold to farmers, and other materials, such as plastic and metal, are bought by rubbish collectors who process it and sell it on.
The Klinik Bumi Ayu is staffed by two doctors, one nurse and two pharmacists and is open daily in the afternoons. Most of the patients are agricultural workers who toil in the rice paddies surrounding Malang, in eastern Java.
On a recent Saturday at the centre, about 10 patients were waiting to be seen by doctors.
A woman held her two-year-old daughter close, wrapped in a sarong, the young girl's eyes puffed up and red. After a quick examination, a doctor diagnosed her with a severe bout of diarrhoea and sent her away with some medicine.
Efriko Septananda, a doctor at the clinic, said common problems people came in with include high blood pressure, diabetes, runny noses and gastroenteritis.
Most earn between 500,000 and one million rupiah a month ($44-88), and would struggle to get good medical treatment if the clinic did not provide it in exchange for rubbish, he said.
- 'Now I can pray normally' -
Free public healthcare does exist in Malang and other parts of Indonesia. But getting access to it is a complicated, highly bureaucratic process, according to Albinsaid.
For Mahmud, treatment at the centre has helped ease his arthritis.
"Before I did not feel well, especially when I had to bend over to pray," he said. "But now I can pray normally."
More than 90 percent of Indonesia's population describe themselves as Muslim.
Albinsaid, who is training to be a doctor but does not treat patients at the clinics himself, said the system has been successful as only 10 to 15 percent of people who bring in garbage use the services.
This leaves enough money to run the centre and fund its development.
He hopes to expand the scheme across Indonesia with clinics planned in three other cities so far, and the government has also taken an interest in getting involved.
For Albinsaid, it is also about giving some of the least privileged in the country greater control of their destinies.
"With these clinics, we can help empower poor people," he said.