The costly mistake happened at Chivas Brothers when the spirit was wrongly discarded down the drain.
Bemused sewage workers contacted bosses at Scottish Water when they noticed a strong smell of whisky coming from the waste water.
Chivas Brothers have now launched an investigation into the incident which they say happened on Tuesday and is being classed as an "accidental loss".
They say there has been no contamination of the River Leven.
The company – whose premium brands include Chivas Regal, Ballantine's, Glen Livet and Royal Salute – employ hundreds at the Dumbarton factory.
A spokeswoman for the firm said: "We are currently investigating an accidental loss on February 26 at our Dumbarton site, when some spirit was released to the local water treatment plant operated by Scottish Water.
"There has been no release of spirit to the River Leven or any other local water course.
"We have informed Scottish Water and all other relevant authorities."
A Scottish Water spokesman said: "Staff at our waste water treatment works were already aware of a problem and were working to identify the source, when contacted by Chivas Brothers.
"We are continuing to monitor our Dumbarton Waste Water Treatment Works to ensure treatment has not been compromised."
It is understood staff from Scottish Water have visited Chivas Brothers to talk about their investigation.
Discharging large volumes of alcohol into the sewer network can have an adverse impact on waste water treatment processes, particularly in cold weather.
Chivas Brothers employs 1600 staff across 32 sites in the UK and its headquarters are in Paisley.
The company has 12 operating malt distilleries, a grain distillery, two gin distilleries and over 300 bonded warehouses, containing an aged inventory of more than six million casks.