Asphalt production is pretty prevalent in today's economy with an estimated 70% of it being used in road construction. Chances are you already call on these accounts or at least have some in your area so specifying out a  Strahman Valves Piston-Type Sampling Valve  should be easy.  

The keys to specifying the right valve for these types of applications are getting the right seals for the temperatures involved as well as getting a valve that won't clog after repeated use.  As you can see in the example below, this was accomplished with high temperature graphite seals and utilizing a full port (same inlet and outlet size) valve. Additionally, one of the advantages of a Strahman Sampling Valve is that the design is inherently non-clogging and self-cleaning with the tight tolerance fit of the body and coupling. Deadspace (places to clog) is also minmized with a one-piece piston design.