Inventory System Unity (Third Person)

I wish to create an inventory system.
I had the idea to have a cauldron have its own inventory. The (third person) player adds objects to that inventory by dropping objects into the pot (hitting the collider of the water, the water is a separate object)
The crafting system uses that inventory to create potions.
The only issue is that I’m very stuck with getting the cauldron to work with an inventory. I already made a UI but I don’t get how to make the cauldron register when the object hits the collider and to add that object …