Any holding tanks for something like that would be in blueprints. Or at least there would be space for those small tanks somewhere inside the aircraft.
I gave up trying for more research once I delved in and found no actual evidence. Of course people do believe in them, and if I was shown real evidence, I’d change my position. So much else to concern myself with... People around here claim they’ve seen them and I never even see contrails; the only planes in the sky here are very small local ones rarely, firefighting helos in the summers, and mil jets on occasion. :-D
Not to mention the piping, valves, control circuits and the switches/computer links to make the whole thing work.
All of which add complexity plus the all-time most hated thing on earth to aircraft design types ---- WEIGHT.
Show this ol' Aero Barrio (if only Flight Testing) guy a C_A owned/operated aircraft dedicated to this sort of thing and I'll cheerfully renounce my Chemtrail Denier status.
Otherwise, those things in the sky behind the high fliers are condensation aka contrails which are benign, unless you're on a bombing mission and those things rat you out to the antiaircraft blokes.
Or you're smoking something really strange before you post about them. /jk