mealy bugs- horticultural oil dunk?

[Kailyn]

hello
I have a mealy bug problem on a few of my plants mostly on a Mtassa Royal robe. I've been told to submerge the plants in soapy water but i've seen little success with the method (my rosemary still has aphids after a solid soaking) and my angraecum still had some mealy bugs after the same treatment. is it ok to dunk the entire plant in a solution of horticultural oil? I've been leaving this one alone while it blooms but its blossoms are pretty much done so i want to kill the bugs and get it in with the rest of my collection.