Every federation has a different view on this, some have natural which means 2 or 3 years and some have pure which means clean forever.
Typically organizations don't test but a few guys, just a piss test, and some "look" really clean and some throw weights up that you sit back and say "just ain't possible."
Just let your conscious be your guide, your body will eventually reach an equilibrium and your body will be back where it wants to be eventually.
I personally wouldn't not compete if you haven't been clean as long as they want you to be unless your really smoking everyone else and have somewhat of an unfair advantage.
There's virtually never a 100% drug-free competiton any place you compete.