The ATC job is exclusively a team activity. Since every job is different, the ATC crew needs to be flexible and adaptable to changes. Intimate knowledge of the ATC's capability is what ConstantinConsulting passed to the local crews in Soyo and Malongo.
Let's keep it simple.
The Cleaning Machines do not mind the confined spaces, they don't mind toxic fumes and the lack of oxygen. So let them do what are designed to do: clear the tanks of all the bad stuff before the ATC crew enters to finish the remaining bit.
When the time comes for the crew to enter the confined space ConstantinConsilting makes sure the place is 100% safe to enter.
Assuming things are functional doesn't go along with ConstantinConsulting.
Seeing is believing!
Test, verify, check, and again double-check this is the way to success.
The practice makes things perfect. The tanks farm offered endless opportunities to exercise the ATC cleaning techniques.