FS19 didn't need a mod in order to unload seeders/sprayer, it was built into it since day one. That said, there are many ways to make a seeder/sprayer unload, Giant's chose to empty into pallets (creates seed/fertilizer pallets, places them on either side of the unit when unloading). This is logical.
When FS19 first came out, I liked the way the seeders/sprayers unloaded and incorporated the same system in FS17 - giving all seeders/sprayers the ability to unload into pallets. I started this by perusing the FillUnit specialization, paying attention to unloadFillUnits(), creating my own pallets for various unloadable fillTypes (I liked the "stacked bag" style pallets for seed/dry fertilizer), etc. This script is a new specialization, gets loaded into seeders/sprayers at the beginning of the game (via another separate registration script).
Only one bit of conflict encountered, with the GameExtension mod, had to incorporate a slight code overwrite/injection from my registration script to alleviate. Forget what the issue was, was probably a showstopper, but the overwrite fixed it. If you have issues when creating your own method, I can look into it the overwrite and pass along the info to you.