The extensive 33-hour cleaning effort will see the tunnel closed to traffic in both directions from 8pm Monday night (April 30) through to 5am Wednesday (May 2), explained Phuket Highways Chief Somwong Lohanut.
The work is being carried out ahead of heavy monsoon rains.
Specifically, the clearing of all litter and rubbish from the drains will help to prevent flooding during especially heavy downpours in the coming months.
Highways Chief Mr Somwong added that workers will take the opportunity of the tunnel being closed to also clean the manholes dotted throughout the tunnel.