The best place to start is with good stool testing - I would highly recommend GI Effects from Metametrix. This test will identify if there is pathogenic involvement - then you can effectively treat. Black-Walnut is ok but will not kill every parasite or bacterial/yeast issues.
The proper way to cleanse the liver is not the Liver Flush which is only adequate for stimulating the gallbladder (stones/sludge) issue. The proper way is liposomal glutathione with a herbal liver cleanse. If you choose not to use gluathione then cysteine would be adequate with some methionine.