I had the same situ.,1 of my 2 Knockoffs got Real Funky!I filled it 1/3 full,poured about 1/2 carton of Morton salt,& shook the daylights out of it,for 5 or so minutes,dumped it,then tossed a box of Baking soda in,then about a pint of Vinegar,Let it foam out,Rinsed it out,while swirling it,2 times over,It was spotless,& Smelled like the plastic it is.When I dumped this thing out,I did it into my trashcans,Sweetens them up,a bit,& kills flies/other nasties!
Good stuff, thanks. Gotta get this done this weekend because I'll be camping the following weekend and want to fill it and carry it with me.