To be fully anonymous:
* Ensure the file you wish to upload does not have hidden meta tags of any kind. Using plain text (.txt) is good too.
* Buy a new budget laptop with wifi capabilities. Around 200-300 should see you ok. Pay in cash.
* Go to Mc.Donalds. Use "their" wifi to connect to the internet. Upload from your car, do not enter the store.
* Burn the laptop.