Fermenter bucket still a bit rank after several cleanings

Brewed my first two batches this month and still trying to figure this process out. I'm using a couple (similar to this, but maybe not the same material) buckets (with spigots) for fermenting. They worked really well and sealed great but after cleaning them, they both still smell like beer. I used Oxiclean and hot water the first time and removed anything that was stuck on the sides with a soft sponge. Thought that would do it but a few days later the bucket still smelled like fermenting wort. Weird. It looks spotless. I haven't scratched the inside as far as I know and the only things that have touched the inside are beer, the spigot, a sponge and oxiclean. I decided to duct tape over the bucket hole, disassemble the spigot entirely, and drop everything in a full bucket of Oxiclean and hot water for a few days to soak. Even after rinsing both buckets a few times, the smell has lessened but still quite noticeable. I'm thinking I may need to bleach it or find a stronger cleaner. Is the aroma issue just typical of plastic buckets or do I need to up my cleaning game?