Seeking help with mod process

I am attempting to recreate the rustic mod in 1.19, but I have hit my first hitch. I am trying to create a block like the crushing tub, but I can't figure out how to make it convert items into fluid when the player jumps on the tub. Any help with this would be greatly appreciated, as I really want to see this mod updated and don't know how to port the original code (it is MIT license)