Understand that Dawn dishwashing liquid is a detergent not a soap. Few, if any, insecticides are effective in controlling Mealybugs. Perhaps this article may be of some help.

http://ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html

I suggest that you make a misting solution with diluted isopropyl so that you can spray the plant on a regular basis, controlling tiny nymphs in the little hidey places. Keep the misting bottle handy and use it every few days. I would not use Dawn, so infamous for causing tissue damage to plants.

Commercial insecticidal soap can be more effective and less damaging.