Anti-graft investigators should be called in to probe why government drain cleaners can escape punishment for not working while on duty, an inquiry said. A Provisional Urban Council investigation into the inquiry's findings also urges the Civil Service Bureau to consider disciplinary action against the workers and their supervisors. The inquiry report found that 15 overnight workers, who were responsible for clearing drains in Kowloon, had 'seriously deviated' from job procedures. The problem had lasted for at least 18 months, despite surprise checks, before the scandal came to light last January, the report states. It reprimands the workers and their supervisors, and criticises former Deputy Director of Urban Services Michael Arnold for obstructing the inquiry. Surprise inspections by some councillors found workers at the department's Mongkok depot were playing cards or sleeping after clearing one drain in the depot. Mr Arnold then banned witness Lo Pui-lam from testifying at an inquiry. The council passed a motion in April to condemn Mr Arnold, who was eventually moved to the Central Policy Unit. At a hearing, Mr Lo testified his colleagues had pumped tap water into tanks to make up their daily quota, cleared drains only once a week instead of every day. His colleagues refused to appear at the hearing and the department also refused any assistance to urge them to testify. Inquiry chairman Kam Nai-wai said: 'The problem involved three teams totalling 15 members and lasted for over a year. But besides Mr Lo, no one has made any complaint. The department has failed to explain to the inquiry why such a situation could be tolerated, or why it was not uncovered, for so long. 'We cannot rule out the possibility the misconduct is of a collective nature and we suggest calling in the Independent Commission Against Corruption.' The average net weight of sludge collected rose 4.5 times to 1.45 tonnes a day after the scandal was exposed. The daily average in 1998 was 320kg and 670kg in 1997. Mr Kam believed there could be many other instances of lax work. A department spokesman said it was not prepared to comment as an internal disciplinary proceeding was under way. The council is expected to endorse the report at a meeting next Tuesday. Last month it was revealed some Mongkok rubbish collectors were found to have idled away almost six hours each shift by eating out or sleeping.