The side products of your reaction, while soluble in water, are not soluble in saturated salt solutions. Your product, while slightly soluble in water, would be much more soluble in an organic solvent like ether or ethyl acetate. Since you haven't mentioned a solvent, I assume you are running the reaction neat?
I would start my workup by diluting with either ethyl acetate or ether, wash with water to remove the COMU decomposition products, then wash with less-than-saturated solutions of sodium bicarbonate (to remove unreacted benzoic acid) and ammonium chloride or HCl (to remove unreacted benzylamine). Then strip off the solvent to recover what should be much cleaner product.