I wonder if you could custom make your own adapter? Go to Home Depot and buy a 3/4 to 1 inch adapter (or the end size you are looking for), take it home put it in a vise or use a drill press to ream out the smaller side to the metric size of the reactor. Hopefully you could find a drill bit or a spade bit to match the OD of the metric, and hopefully find an adapter at HD with enough plastic available to grind a little away. Glue the crap out of it, and give it a leak test....