That is basically the answer I found. Some people talked about soaking in vinegar first but still was kind of crap. I also read something about maybe naphta not being good to pull with sodium carbonate, maybe that is bs but I've decided to just do what most people do and just use the lye. I'm a little concerned with how I'll manage to find suitable lye and naphta here. A cursory look at the lye for sale at supermarkets showed other stuff added to it so I'm not sure it can be used. I'm thinking of using Zippo lighterfluid for naphta but I also don't know if the kind they have here is suitable (there is no "ingredient list" in online stores and haven't seen it for sale offline).

Also, my MHRB is a fine powder. Would that make much difference?