Pictured above is my set up, consisting of a vacuum pump and hose connected to a piece of iron pipe. The bottom of the pipe is closed off, so that when the pump is engaged a strong vacuum pulls from the top of the vertical pipe. Into the open pipe I place the form that I am going to use, in this case a life casting of a woman's face poured in plaster, with a smaller diameter iron pipe protruding from the bottom.
The smaller pipe inside the larger pipe still allows the vacuum to suck air. For my leather I have chosen a very thin lambskin, as it will absorb water when immersed, and then become plastic. At the same time it won't allow any air to pass through it, so that when I firmly wrap the lambskin around the larger pipe, the vacuum pulls the damp leather down around the face.
To ensure a good pulldown all around, I drilled small holes in the recesses of the face: The inside corners of the eyes, the nostrils, and the outer corners of the mouth. I also worked it with some dull metal tools to help the leather conform.