These 2 other industries are both totally different in the products they manufacture and the methods they employ to produce them.
The Paint industry manufactures all types of protective coating, some water soluble but the majority not, requiring a solvent to be used to successfully remove the product from the internal surfaces of the Mixing Tanks. This then brings the requirement for the cleaning to be done under a Nitrogen blanket to stop any sparks being generated from a static discharge as well as cleaning head technology that is fully compliant with ATEX equipment requirements.
The best way to make sure a clean of the application is successful is 1, make sure the tank is cleaned before the product is starting to dry, 2) keep the cleaning heads out of the paint/product by use of a retractable system or to make sure dried product cannot jam/block the head.
In the Paper industry it is a matter of cleaning large White Water Storage Tanks, Pulpers, Pulp Tanks and Product Mixing Tanks etc of which can sometimes can be open topped, but all these applications can be cleaned with careful choice of cleaning head technology and mounting positions for the head.
There really is no requirement for anyone to enter a tank anymore to clean it, which has been a big step forward in Health and Safety for this industry.