insecticidal soap bath (rather than spray)?

ten plants worth of spray later, my hands are wondering! has anyone tried a bath/dunk/dip for getting rid of mealybugs or scale, rather than spray?

i would be okay with spray if we were talking about, like, a snake plant, where the leaves are pretty easy to handle. but i'm working with a bunch of viny hoya plants and i'm sure i'm missing some books and crannies, so i was wondering if it would be possible to dilute the soap and dip the vines (or the whole plant, when repotting) instead.

has anyone tried this? if so, has it worked, and at what dilution?