If you get paid money legally and just… transfer it a bunch through various banking accounts or similar. That is obviously not illegal in any way.
If you get paid money legally and then say, “buy a lot of car washes” at the car wash your cousin owns and then he pays you the money back and you two don’t report that to the IRS, that would be tax fraud (though laws on “gifting” money get pretty vague)
Basically, it’s really hard to somehow illegally “launder” clean money