The issue is the large number of window cleaners with a full 1000ltr ibc in the back thats tied down with an old boot lace and goes out through the windscreen in a smack the insurance companies judge us all by this sort of practice and we all suffer
No window cleaner has a 1000 ltr tank. I can work all day with a 250 litre tank. Also most are professionally fitted because they also have pumps, flow, controllers di vessels etc. Many of the vans are bought or leased with the tanks already installed. Window cleaners generally earn good enough money to have proper setups.
I have never seen a window cleaner with an ibc in the back, the only people I have seen with them are wheelie bin cleaners and pikey drive cleaners.
Ironically, you only have to declare it if it is fitted, which seems bizarre, if its not fitted its just goods in transit