but can someone tell me how they do it if its not in the fuel and not in barrels in the plane itself ?
Hi Eric and welcome to the forum.
Nobody is actually "doing it". What you see is just a natural result of engine powered aircraft flying in very cold moist air at high altitude.
It's like a speed boat leaving a white wake. No-one is intentionally "making" the white wake, it's just a natural unavoidable side effect of the crafts' high speed passage.
When jets fly their engines create water and that gets added to lots of water already in the sky , triggering it to condense on the small volumes of soot in the exhaust. If the air is really cold and humid up there the trails will persist a long time. If it's warmer and drier up there the trail won't last so long.
Unfortunately you are misunderstanding the fact that normal passenger planes regularly leave very long persistent condensation trails. They are not spraying anything. They don't need to carry anything in tanks to make trails other than unmodified fuel to make the plane fly. It's just ice crystals and if you explore this forum further you will discover more about the subject, but perhaps most concisely if you visit the sister site contrailscience.com
Please have a look at the Video I posted above called Boeing promo film 707 year one.
Whilst I posted It in regards to the ballast certification tanks used for simulating the mass of passengers, before the plane is allowed to carry passengers, notice how that promotional film, shown as a "short" accompanied by a major theatrical release clearly shows a normal 1960 passenger jet leaving long trails.
Notice how the narrator isn't mystified by the trail. Notice how He doesn't say: "Oh my god we're doomed someone is spraying poison from this new passenger jet". He knew and the public would have understood it was simply a condensation trail, a sight already familiar to the public from propeller driven passenger airliners:
This film would have been seen by millions of members of the public who also would have seen nothing strange about the trails.
Here's a famous Pan Am promotional film from decades ago.
Anything look familiar?
these very old films show that passenger airliners made very long trails decades ago, at a time when chemtrail believers insist no such thing occurred because they never noticed them in the past.
What you see in the sky was a common sight decades ago.
Unfortunately a hoax has arisen and people who never paid attention to these common trails previously, have only started to notice them now as attention has been drawn to them by fearmongers.
The same phenomenon of people not noticing incredibly obvious day to day things and thinking them new and suspicious only when someone specifically points them out is well illustrated by the Seattle windshield pitting "epidemic" http://www.neatorama.com/2012/09/17/The-Great-Seattle-Windshield-Epidemic/