Minecraft Version: 1.12.2
Forge Build: 2554
Mod Version: 0.4.3

Trying something like the following throws up the error that the method exists but the inputs are wrong. However, it appears to follow the wiki exactly, so have I made a mistake or is there an error in the mod?

CrushingTub.removeRecipe(rustic:ironberry_juice, rustic:ironberries);

The wiki must not be up to date for the latest version of CraftTweaker. Looking at the CraftTweaker2 wiki, I can verify that you're inputting the fluids as items. Fluids use <liquid:olive_oil>, not 'rustic:olive_oil' (and naturally the same goes for fluids besides olive oil, just replace the fluid name).