Mr Sefton said up to 10 people a week were trying to cheat the tests - with most relying on a friend to provide a clean sample.
"This is usually concealed down the donor's pants in small bottles, condoms or similar receptacles."
Mr Sefton said the level of cheating depended on the type of industry, but most occurred at pre-employment tests.
"The donor is aware that they have a drug test to complete and they come prepared to try and cheat. In a busy week we may have anywhere from three to 10 cheats."
People also tried adding chemicals such as bleach to urine to try to mask drug use and others took cleansing or flushing pills available at various health stores.
"However we still have a number of people fail the test and get quite upset that the flushing product they purchased hasn't worked."
Testing options included pre-employment, random, post-incident or accident and reasonable cause testing - when an employee was displaying recognised indicators or patterns of drug use.
He said the fact people attempted to cheat workplace drug tests was "a real shame".
"They don't seem to realise, or care, that drug testing is all about providing a safe working environment," he said.
Those caught trying to cheat drug tests were usually fired.
"It is a serious issue when someone is willingly jeopardising safety in the workplace," he said.
