Hmmmm.....Mine is plastic like too....Not sure what kind tho....Mine was from Boost Bottle Industries.....I was gonna make a flat spot in it to put a drain but when I realized it was not metal I put the hammer away...
Made my own boost bottle out of a the outside casing of an old shock absorber and cut it down to be the right capacity, welded up end cap where I'd cut off the internal rod the drilled and tapped a whole in the side at end so that any accumulated fuel could drain made a bracket to fit it onto the cross bar above the carby, and works just fine. Gets me on the pipe real quick.
Boost Bottles are choice. The whole process only took me about a couple of hours to do.