Double Boiler Pot Homemade Double Boiler?

Homemade double boiler? - double boiler pot

I offer these things with chocolate on the anniversary of my mother and I have a bath. The problem is that I do not. How do I make a bath together with the pots and pans? Is it fair to put a small container in a large pot. It covers the entire upper or will leave an opening to allow steam to? no help at all to help. Thanks in advance