know somebody/something inside out
know (someone or something) inside out
To know everything or nearly about someone or something; to be thoroughly familiar with someone or something. I've read this book so many times that I know it inside out. If you study this material for weeks, you'll know it inside out by the test date. I just think you should know a person inside out before you decide to marry them.
know something inside out
to know something thoroughly; to know about something thoroughly. I know my geometry inside out. I studied and studied for my driver's test until I knew the rules inside out.