Troy Mathieson, 23 and Hughie Morton, 21 likely died within minutes of being forced under floodwaters in the Townsville suburb of Aitkenvale early on February 4, 2019.
At around 3.30am, the pair were interrupted by an unmarked police car while at the local Dan Murphy's store, inquest findings delivered on Thursday say.
A disaster had been declared in the region following extreme monsoon activity in late January.
After being discovered, the men jumped a fence at the rear of the property and entered a flooded drain - the depth of which was estimated to be approaching two metres.
Flood waters pushed them into the pipes of a submerged culvert running underneath Ross River Road, and exiting near the Aitkenvale Library.
Their bodies were found nearby the following day.
In his findings, State Coroner Terry Ryan concluded that declaring the pair missing instead of wanted would not have prevented the deaths.
The inquest heard evidence that the shortest time someone could emerge from the other side of the 170-metre culvert was one minute.
A police diver told a hearing that in the same situation, he would not have been able to hold his breath for much longer than 30 seconds.
It was also not possible to know if a grate installed on the culvert could have changed the outcome, considering factors such as water flow, debris in the water and swimming ability.
Additionally, extra signs or fences would not have prevented a person determined to enter the flooding drain from doing so, the coroner found.
