Deep Cleaning is one of the many optional side missions within Ghostwire: Tokyo. It involves having to find a specific spirit.
The quest giver for this one is a man known as Old Man Concerned About Water
SIDE QUEST: Deep Cleaning
QUEST GIVER: Old Man Concerned About Water
A MAZE OF DEATH: Make Your Way To Shiroyama Shrine
REWARDS: 7,500 Meika, 1,000 Spirits
The Deep Cleaning side mission can be found to the south west of Namita Shrine, inside the building here. Once inside search for the Old Man Concerned About Water
Upon speaking with the concerned man he will mention that the water flow has stopped and that emotions are running high.
FIND A PLACE WITH LOTS OF STILL WATER
After successfully accepting the quest there will be a large green marker on the map, this is our next destination. It is to the west of our current location.
Once you arrive at this next destination you will find yourself at a Bathhouse. Head inside.
FIND THE SOURCE OF THE CORRUPTION
Inside the Bathhouse continue on into the backroom and eliminate the tree blocking the path. The doorway to the right will then become blocked leaving us with only one other alternative.
Head through the door on the left, we will then be in a hallway. This hallway will then lead to another door.
DEFEAT ALL ENEMIES
Eliminate the threat.