How much postage should I put on the return envelope? It is very frustrating that I cannot find this online. It is a bubble-wrap envelope which varies more than a quarter inch in thickness. So it's a package? It has only the two swabs inside, but the label on the plastic bag reads "Hazardous Material" which puts a simple first-class postage in question. Why don't they simply supply a postpaid envelope and save what has probably added up to thousands of hours of their customers trying to figure out the appropriate postage?