Thanks for writing. Unfortuantely, there aren't a lot of good solutions for dealing with Japanese beetles right now. Because the insects are so mobile, sprays aren't particularly reliable. You can kill the ones in your yard one day by spraying, but there will be a new crop the next day.
If you're going to spray, look for a product that contains neem oil; you may find a variety of brands at your local garden center or nursery. I'd avoid the dishsoap as it the soap can actually damage some plant varieties.
---Justin, Senior Garden Editor, BHG.com