Definitely not snorting. Idk about rectal since benzos typically aren't water soluble and idk how that affects absorption since I've never looked into it.
Best way to take is oral, sublimgualy. Just leave it under your tongue for as long as you can, till it disolves.
Don't snort it...total waste.
Plugging...don't know for sure, but I'm guessing yes. I plug zopiclone (a benzo-like sleeper) on occasion & it works excellenty plugged rather eaten.
Yes, crushing and taking it sublingually will increase the onset. I think that the BA will still be about the same as oral, so the duration should be about the same as crused and swallowed diazepam.
Valium tastes a lot better than xanax though. I ususally allow my diazepam to sit under my tongue for a couple of minuted before swallowing it, and it isn't that bad of a taste.