I worked for a well off man that spoiled one of his sons terribly. Aforementioned son was pissed off because of some perceived slight, got drunk and dumped half a bag of calf pellets down the tank of his JD 4430, and most of a 2.5 gallon jug of glyphosate in the tank of his feed truck that was parked there (Chevy 3500HD, 454 gasser).
I pulled the tank out of the JD and sent it out for cleaning, eventually got it sorted. That was 10 years ago and up until recently was still clearing feed muck out of the sediment screen occasionally.
The truck was in way worse shape, I didn't have time to work on it, and it bounced around several different shops. The whole fuel system was trashed, and it stuck most of the intake valves. Last I knew he gave it to a neighbor that eventually got it running and sold it.
Nobody knew the equipment had been messed with, he tried to move the tractor to another farm and made it a couple miles down the road. I was able to swap the filters and backflush the lines enough to get it home, at that time I noticed the pellet crumbs near the filler cap. No good reason for those to be there.
The truck supposedly started for a little bit and quit right away, we spent quite a bit of time trying to figure out what went wrong, it was during a terrible cold spell and suspected ice. I took a fuel sample from the rail and noticed the fuel was very slick and slippery, smelled like spray chemical. Then I found the empty gly jug tossed in the corner with a funnel next to it.