Gokkun just means the sound for Gulp; It is an onomatopoeia (https://en.wikipedia.org/wiki/Onomatopoeia)
Bukkake essentially means Splash
Gokkun is swallowing, Bukkake is facials
Sometimes gokkun and bukkake exist in the same video, but Putalocura's "Spanish Bukkake" has almost always been about swallowing, not facials, so it's largely a misnomer. PremiumBukkake's content so far is almost entirely swallowing, so Bukkake is a bit of misnomer again. Although, there are scenes they've released that feature bukkake, like Angela's.
The material should have been called SpanishGokkun and PremiumGokkun, but this is a largely useless and unimportant semantic issue.
Nothing about gokkun requires drinking from a vessel or container