Steamed? Why and how? What if he needs an quantity we might describe as
"five bath tubs full"?

Steamed to reduce pathogens and eliminate weed seed. Could be solarized at
home.

And we steamed the material by putting a pipe fitted for a low pressure
steam connection into a spreader plate cut to fit the bottom of a metal
trash can. Insert steam pipe, fill with mixture (we used a manual cement
mixer to mix soil), cover the can with a metal two-piece collar that
was cut to fit around the pipe, and steam to an internal temperature of
160oF. Cooled for at least a week before using.

And yes, it was a large research university.