There are a number of different eductors/penductors on the market so the sizes may vary. I know the ones that I used to use connected to 3/4" loc line which is 3/4" NPT which if you measure the threads is almost exactly 1" OD, but that's just how PVC sizes work.
BTW, if you don't already have them, I have a pair I'd sell cheap (and would be willing to let you try out and pay later if you like them).