Drainvac recently updated their lineup. I'm not sure what's new about them. Sadly their Booster models have been discontinued, I've been wanting to try those out to see how powerful they really are like the DV1R18 for example since Drainvac isn't common in my area.
I don't know about Purvac, they don't have their own website so it's possible that Thinkvacuums owns that brand.