I see... if you've done that, you SHOULD have automatically collected some Hardened Black Sludge.
If you don't have any, you lost it or sold it or something... then I'm afraid you can't get any more at the moment. Just to check though, you mean the 'black sludge' and not the hardened slug secretions, yeah? 'cause if you need that, you can get it from fighting slugs in the jungle.