Police made the bust - the second-largest ever made in Victoria - in July, seizing 4.125 tones of the drug at a warehouse in Brooklyn after a tip of from the Australian Federal Police.

1,4-butanediol is closely related to GHB and converts to the drug when ingested.

About 165kg of hypophosphorous acid - a chemical commonly used to make methamphetamines - was also seized.

"Ultimately, this is a syndicate who could have caused immense harm within Victoria through the sale of these drugs to the community," Victoria Police Assistant Commissioner Robert Hill said.

Three men were arrested by police in July and another two properties in Ardeer were searched.

Police say they found commercial quantities of steroids, drug-making chemicals, MDMA tablets, cash, cannabis and a substantial quantity of glassware at one of the properties.

Two of the men arrested, both 29, were charged with a string of offences including conspiring to traffic a large commercial quantity of drug of dependence and possessing precursor chemicals.

Both men will reappear in Melbourne Magistrates' Court on January 27.

Another man, aged 28 from Airport West, facing the same charges will also appear before court on January 27 for a committal hearing.

A fourth man, 31, from West Footscray was charged with cultivating cannabis and will appear in Melbourne Magistrates Court on February 21.

Australian Associated Press