>Can he guarantee his pressure cooker autoclave works, and if so how?
Autoclave tape
Just because one utilizes alternative materials does not mean the scientific method goes out the window. Finding a repeatable process is paramount.
Also, many of these DIYbio projects take advantage of methods used in labs for years. There are multitudes of testing procedures, validations, ect that enable one to see if their over the counter laxative is up to par.