Q: "What do I need to do to make sure I'm not doing anything illegal here?"
R: You can not put your plan into action. What you're planning to do is called "reverse passing off" and is unlawful. Read the many questions and answers already posted about this type of endeavor [use the link below].
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
You could do what you want to do by negotiating an agreement whereby you license the product for the use you wish. Hire a lawyer to advise you.
This response does not create an attorney-client relationship. Unless you are already a client of the Mallory Law Group, pursuant to an executed employment agreement, you should not use, interpret, or rely on this response as legal advice or opinion. Do not act on any information in this response without seeking legal advice. Earl K. Mallory firstname.lastname@example.org (561)743-3708.
As a franchise attorney, this is a bit out of my area of expertise - helping companies franchise a business concept and advising individuals, as a franchise expert, on making franchise investments. However, I can say the following.
I agree with my other colleagues on this. The big issue is reverse palming off. You would either need to negotiate a license with the household product brand - and once they find out what its for, if it's a good idea they'll just run with it themselves. Or you'll need to formulate your own "recipe" and then brand it yourself.
Either way, you need the services of a good IP attorney to guide you.
Best of luck,
Kevin B. Murphy, B.S., M.B.A., J.D.
Franchise Attorney & Franchise Expert
Director of Operations - Mr. Franchise
FRANCHISE FOUNDATIONS APC