Just after the footpath beside the school passes into the cool late afternoon shadows, a gentle cracking sound signals that Doud Sebet has arrived.
He sits on a piece of cardboard, with one long leg out in front of him and the other tucked underneath.
From a white sack, Sebet retrieves metal drink cans that other people have thrown away. He slowly places each of them on one brick and hammers down on them with another. The flattened coloured circles collect in front of him.
He and an increasing number of others are scouring garbage to make a living in the troubled economy of Sudan, a country ranked near the bottom of a United Nations human development index measuring income, health and education.
"The people of this area are living in luxury," Sebet says in his favourite hunting ground, the Khartoum 2 district where foreign ambassadors and wealthy business people live.
"There are many restaurants," he says, making it fertile territory for a scavenger like Sebet who also collects discarded plastic water bottles.
He marvels that some people drink water from a sealed, disposable container. In poorer parts of the city, water is delivered in a tank pulled by a donkey.
It is not just the rich areas that are targeted by scavengers -- the more down-to-earth community of Khartoum's twin city of Omdurman is also rich pickings.
A growing number of people are turning to the city's rubbish for income in a "static economy" which is failing to create new jobs, says University of Khartoum economist Mohammed Eljack Ahmed.
"Within this economic atmosphere this is a good alternative for them," he says.
Sudanese have struggled to cope with soaring inflation and a weakened currency since South Sudan separated in July 2011 with about 75 percent of united Sudan's oil production.
The lost crude accounted for most of Khartoum's export earnings and half of its fiscal revenues.
Inflation is close to 40 percent, and Ahmed estimates that unemployment exceeds 30 percent.
"We are suffering," says Sebet, who is over 60 years old.
His breath smells of alcohol, and Khartoum's ever-present desert sand has stained brown his white jalabiya robe.
Sebet says he can earn 400 pounds (about $60) a month by recovering the cans and selling them to a company.
A native of South Sudan, he says he lost his government employment many years ago and then turned to hauling goods for merchants until illness forced him to stop.
Now, this is his main job, helping to support a teenage daughter who lives with him at their home made from grass and wood in the city's south.
Every morning Sebet travels by bus to scour the trash of Khartoum's elite. When he is done, he sits in the shade of the school overlooked by a high rise apartment block where foreign diplomats live.
He shakes the cola containers and if there is anything inside he tilts his head back and drinks before methodically bearing down on the can with a brick.
Sebet is a veteran of this dirty business but others have turned to it more recently.
"I have been collecting these things for seven months," says 26-year-old Mohammed Adam, in Omdurman.
Another young man, Osman Haroun, 25, says he can make 10 or 15 pounds a day scavenging.
"We choose specific areas, where the rich people live," he says atop a donkey cart which he and his work partner bought to make their job easier.
"Before that, I didn't have permanent work," Haroun says.
Another scavenger in Omdurman, Omar Muhajir, 56, said rubbish collection helps to support his five children -- whom he hopes will have a better life than his.
"I don't want them to have to work like this, collecting things from the garbage. On the other hand, it's better than sitting around without a job," he says.
The International Monetary Fund (IMF) estimated that Sudan's economy would get a boost of nearly $500 million (375 million euros) this year and about $1.5 billion in 2014 under an agreement between the two countries for South Sudanese oil fees and a package to compensate for the loss of the South's oil at separation.
This could help ease the deterioration in living standards for ordinary Sudanese like Sebet.
"If this windfall is used wisely... it will contain the rising cost of living which has been crippling everyone but especially the poorest," an IMF official told AFP in May.
But new economic uncertainty emerged this month when Sudan began to stop the flow of oil.
President Omar al-Bashir ordered the closure of the pipelines carrying South Sudanese crude because of alleged southern support for rebels in the north.
After South Sudan's separation, the oil refineries and export pipelines stayed under Khartoum's jurisdiction. The South halted crude production early last year during a dispute over fees for its use of the infrastructure.
Southern production resumed in April and the oil had been slowly making its way toward the Red Sea export terminal before Bashir's surprise order to close the line within 60 days.
If implemented, the oil compensation package would last for less than four years but the revenues would "provide a very valuable breathing space" for an economy which must be restructured, including through the revitalisation of neglected sectors like agriculture, the IMF official said.
Unless the damaged farm and industrial sectors can assume a significant economic role generating employment, the long-awaited oil revenue, despite its fiscal importance, will not be enough to help Sebet and the other scavengers, says the university economist, Ahmed.
Sebet has not heard about the now-uncertain oil deal with South Sudan.
His left shoulder bears the weight of three sacks of garbage as he slowly staggers off, another day's work done.