We have a yearly Visual and 4 year Hydro. Al tanks are uncommon so we don't see many tanks with visual plus. I will look for tampering with the valve. I.E a tank valve that has been removed between official inspections. For the remainder I will look at the regulations as laid down by SANS19 that determine the guidelines on what is acceptable in terms or rust. If i am in doubt i will drop the boot and that will give me an indication as to how the tank has been looked after. Scuba is inherently dangerous and so is filling tanks, but in the same way that I try to become a better diver by participating in discussions and minimizing my risk, i also do the same when filling tanks. I just felt it was important here to express my view as a compressor operator. I don't discriminate on age come and stand beside me and have a chat whilst i fill your tank and there is likely to be no issue.
How do you tell if the valve has been removed?