Is it plastic or metal? Mine is plastic and I soak the pieces in a bowl of water overnight then rinse in the morning and let them air dry. Metal you'd have to me more careful with. You could use the same procedure, but watch the timeline and keep it as short as possible and then put them into the oven for a few minutes to dry.
I have a metal one (Makins) and I wash it thoroughly with warm water and soap. If th substance refuses to come out, I DO soak it for a couple of hours or even overnight and its fine. I have never ran into the problem of rusting at all. I have had it for years
I can do ALL things Through Christ who strengthens ME!!! CAKE IS MY LIFE!!!!