Stubborn Aphids

[Nanotyrannus]

Hi all. I recently discovered that one of my newly purchased herbs was contaminated with aphids. They've jumped to a couple of my downstairs plants, including a Den. kingianum. I've been spraying them every few days with soap solution but they're still kicking.

I want to take this to the next level and just submerge the entire orchid in soap solution to make sure every crevice is treated. Is this advisable? So far the orchid seems unaffected, however I don't know how the roots will react to the soap.