When Chinese official Zhou Jianhua refused to tell Communist Party investigators he had received massive bribes, he says they beat him and forced him to drink toilet water until he confessed.

As a crackdown on corruption pushed by Chinese President Xi Jinping ensnares a growing list of senior officials, Zhou's account -- in a recording obtained by AFP -- offers a rare glimpse inside the ruling Party's opaque internal disciplinary system.

Lawyers say his case demonstrates how the faction-riven graft investigations can mask power struggles and are carried out with little respect for the law.

"They used my relatives as hostages, and tortured me unrelentingly until I accepted the fabricated charges," Zhou -- handed a suspended death sentence earlier this year -- told his lawyers in a recorded meeting.

The Party's internal justice system, known as "shuanggui", operates without oversight from judicial authorities and has been increasingly criticised by China's legal community.

More than 15 officials have reportedly died from abuses in "shuanggui" since 2007.

Xi has vowed to take down high-ranking "tigers" as well as low-level "flies" in an anti-corruption push introduced in response to widespread public anger over endemic graft.

Zhou's case was thrust into the spotlight last month when one such tiger -- the former top Communist official in Jiangxi province, Su Rong -- was placed under investigation.

Zhou says his own fall came swiftly after he accused Su's wife of corruption, and was payback from his party superior.

- Red envelopes -

For years Zhou was a loyal Communist Party member and successful bureaucrat in Xinyu in Jiangxi, known for its enormous steel plant, where he rose to become head of the city People's Congress, the local legislature.

Like his colleagues, he earned little but amassed enough money -- sometimes through illicit means -- for his wife to travel to Britain and other countries.

But in 2011 Zhou began to suspect he might be targeted by an inquiry, and took the risky step of telling a Party anti-corruption team that Su's wife had been illegally profiting from land deals in Xinyu.

Weeks later, several of Zhou's associates were taken into police custody and he was informed that Su had ordered the same team to investigate him.

In January 2012 Communist officials detained Zhou and took him to a centre where he would be held for nearly six months without any access to a lawyer, normal practice under "shuanggui".

"He felt that because he reported Su Rong's wife, he was being targeted as revenge," said Zhou Ze, one of China's most outspoken human rights lawyers, who now represents the former bureaucrat.

Zhou told investigators that he had accepted around 600,000 yuan ($100,000) in bribes, saying this was customary among local officials, who each New Year exchange red envelopes bursting with cash.

"Everyone takes (red envelopes), so I took them too," Zhou admitted in a written account confirmed by Zhou Ze.

But when he refused to confess to larger bribes of around 10 million yuan, the physical abuse began.

"I was beaten, and finally they took me to a toilet, forced my head into a toilet bowl, and forced me to drink the water," he said in an interview recorded at a detention centre in March and made available online. Its veracity was confirmed by his lawyer.

"I knew that if I didn't confess, my wife would face prosecution, but if I did confess, I'd have stains on my reputation I could never wash off."

Meanwhile, several associates said they were also forced into providing evidence against Zhou.

"After days of mistreatment when I was at my wits' end, I confessed to giving Zhou's wife 140,000 yuan," Yang Peng, the owner of an upmarket hotel in Xinyu who was detained for three months, wrote in a statement posted online.

Zhou Jianhua says he gave in and offered a confession on Tomb Sweeping Day, when Chinese people commemorate family ties by sprucing up their relatives' graves.

"I cried because I knew that writing a confession would have serious repercussions," he said.

- Howled with indignation -

Zhou says Party officials warned him that his wife would be targeted if he renounced his confession, and he was found guilty at trial -- as are more than 99.9 percent of criminal accused in China.

In January the court announced a suspended death sentence -- usually commuted to life in prison.

But while in detention Zhou had been chronicling details of Su Rong's alleged crimes on the back of empty cigarette boxes, smuggled out of a detention centre by his ex-wife and other visitors.

They in turn passed the accusations to Beijing officials, including members of the Central Commission for Discipline Inspection (CCDI), the body that runs the "shuanggui" system.

Last month the CCDI announced Su was under investigation for "severe discipline violations", generally a euphemism for graft. Days later he was sacked from his central government post as vice-chairman of the CPPCC, a discussion body that is part of the Communist-controlled machinery of state.

At the time he was the highest-ranking official to fall in Xi's much-publicised anti-corruption drive, which has since claimed former top general Xu Caihou.

Earlier, Zhou's family asked Zhou Ze to lead the defence at his appeal in May, but officials denied him access to the court.

Instead he stood outside the building's white romanesque facade holding a sign reading "Jiangxi high court, I still have the right to defend my client."

Inside, a state-appointed lawyer spent just eight minutes presenting an appeal, while the court was packed with plain-clothes police, according to lawyer You Feizhu, who entered by posing as a relative.

The defendant howled with indignation and began to sing the Communist anthem the "Internationale", he added.

"The court violated my client's rights to a defence," Zhou Ze said.

The appeal decision has yet to be announced, but despite Su's fall the lawyer remained pessimistic.

"These cases are political," he said.