The warehouse measures 700,000 sq ft and some of the 1,200 workers face a ten minute, quarter-of-a-mile walk to two toilets on the ground floor of the four-storey building.
Undercover investigator James Bloodworth said: “For those of us who worked on the top floor, the closest toilets were down four flights of stairs.”
Mr Bloodworth, who worked ten-hour shifts as a picker selecting goods for despatch, walked ten miles a day in the job to research for a book on low-wage Britain.
He claimed workers were continually monitored for time wasting by supervisors.
It meant workers operated a “toilet bottle” system.
Mr Bloodworth said: “People just peed in bottles because they lived in fear of being disciplined over ‘idle time’ and losing their jobs just because they needed the loo.”
He said the warehouse in Rugeley, Staffs, is like a prison with airport-style security scanners where workers are checked and patted down in case they steal.
Hoodies and sunglasses were banned along with mobile phones as a security measure, he said.
An Amazon spokesman said: “Amazon ensures all of its associates have easy access to toilet facilities which are just a short walk from where they are working.
“Amazon provides a safe and positive workplace for thousands of people across the UK with competitive pay and benefits from day one.
“We have a focus on ensuring we provide a great environment for all our employees and last month Amazon was named by LinkedIn as the 7th most sought after place to work in the UK and ranked first place in the US.”