Um, I never had that issue. I would try bleach. They say not to bleach, but I found that adding about 1/4 cup of bleach every 2-3 weeks really helped with smell.
I would try blue Dawn first and then try the bleach.
I would also rinse them every single night (we use a bucket in the tub, or you can just rinse them in the sink or something) and consider drying them in the dryer every 2-3 washes if you can. I don't know much about Bum Genius.