While I haven't Done this Myself I would think if you cleaned the Tank good, then filled it with water and let it sit a Few Days weeks, and took a water Sample and had it tested I think the Tank would be Fine, biggest places of concern would be plumbing connections, seals, gaskets, places where things can be caught in them, there are lots of people using repurposed stainless Tanks such as old firetruck tankers and I am certain that they cant know for sure w/o a doubt what was in it.
What is the chemical makeup of liquid fertilizer?
Nate Hutchins
Nate & Kate's Maple
2022 1000 taps?
3x10 Intensofire
20x36 sugarhouse
CDL 600gph RO
A wife and 2 kids.