FDev told earlier its not an exploit. But yes its a strange way / an alternative solution if resources are low (this method is first used by some Colonia players mostly for picking up tritium at the last Colonia Bridge station and then selling it to other players from their carriers).
Frankly, I think FDev has got that completely and utterly wrong... but when a fix Outbreak Massacres is still outstanding umpteen years later, I have no confidence of this one ever being assessed correctly, let alone fixed.
Washing things through the secure storage to make them clean for use? Fine.
But the rule for missions is: anything that leaves the source cargo depot and doesn't make it to the destination depot will accrue a fine. It literally says this in a message when you fail to shift everything for a mission under any other circumstance. So regardless of how you wash it through the secure storage, that equation where you are fined for the cargo that does not make it to the destination depot is not satisfied... that's clearly broken.
It's impossible to read the below:
And suggest that, without an
appeal to authority fallacy, washing the cargo through the secure storage should invalidate that mission condition.
I would happily wager that whatever FDev rep said this was OK misread the issue and was stating that having the cargo come out "legal" on the other side was ok. The fact this seems to work for Wing missions but not Solo missions smells of oversight, considering there's numerous other inconsistencies between wing/non-wing missions. And when you start to look closer at the mechanics of wing missions through a critical lens, it reeks of oversight.
But whatever... if I was obnoxious enough to tag CMs in my posts I'd probably get accused of being the fun police... who'd've thought bugreports could be griefing right?