As a native English speaker (Australia) I've always known and used the expression "to know something inside out", meaning "to know thoroughly".
Just now when editing a post on another SE site that seemed to be written by a non-native speaker I was going to change "to know something inside and out" to "to know something inside out" but thought I'd check first.
I knew "inside and out" to have a different meaning and usage such as "The vehicle was fully restored inside and out".
I was surprised to find the English Wiktionary has a main entry under "to know something inside and out" and a stub entry only for "to know something inside a" declaring it to be a variant of the former!
This was contradicted by a Google search saying the version without "and" was a lot more popular, but a Google Ngram search seemed to suggest that the two had each gone up and down in popularity over time. So I decided this was all inconclusive.
So what do real/reliable/print dictionaries and other sources have to say about the matter? Are both considered OK, is one preferred, is one Euro-English that made it into the English Wiktionary, or has the expression changed over time, or does it vary by region?