Is it possible for a person who doesn't own the chest to drain someone else's chest using a funnel, could you fix this?
Reproduction -
1 - create a chest with protection from one person X
2 - person Y places funnel under person X's chest
3 - person X's chest is drained

Yeah, that's something I can't control maybe use a plugin like WorldGuard or something to control what blocks players can place.

good idea, I did it to solve it, but thanks