Dude don't smoke it chuck it. You don't know what substance it's been soaked in, but the likelihood is, smoking it would not be very wise.
Oil/petrol etc is all carcinogenic. Chuck it or sell it to someone who is aware of the risks and doesn't give a fuck. Just like a sold my mate my old aluminium space case grinder when i got myself a titanium lol i told him the risks of the aluminium particles coming off but he didn't give a shit.. his choice. Possibly slightly immoral of me but oh well.
Anyway yea, if you care about your health don't smoke it man
Edit - i suppose you could water cure it, but i don't know how effective it would be. To do this you need to keep all of it contained in water making sure none is touching air. Replace the water every day for 3-6 days. then take it out dry it.