"The glass is being used for drinking."
Translation:Le verre sert à boire.
Could one use a reflexive construction here? Something like "le verre se utilise pour boire"?
This makes me think yes:
You don't, I believe. If it was truly necessary to specify the difference, I believe you say "en train de (+inf)" ("in the process of" or "in the middle of") to emphasize that it is happening right now. I think it would be "le verre est en train de servir a boire" if you needed to indicate that it is happening right now. I could be wrong, so other people please chime in, though.
"Est servir" isn't grammatically correct, but "pour boire" seems fine.
If you said "Le verre est servi pour boire," it would translate "The glass was used for drinking." Servir is a verb in french for "to serve", but it can also tell what something serves to do, like in this case. "The glass 'serves' for drinking."