I have a post cleanin yer mud jug, on guy said he puts mouth wash in it. I tell ya what. I wash mine out, then put a half oz of mint mouth wash in it. Dude, even after a couple of days it smells like mouth wash. hope this helps!!
I've heard some coffee ground in the bottom of it helps too.
i have heard that backing soda helps its worth a shot have not got mine yet but ill go with the mouthwash trick first!!