Ha! Not at all helpful. Of course it gets cleaned. There is likely some sort of bacteria that's causing the smell and I am curious if others have found simple solutions at address through additives or otherwise
Run activated carbon in your tanks to avoid any odor anomalies, I hope it is not toxic at all, in any case the carbon will help you, maybe filling the Rubbermaid with plain water for a few days will help you get rid of something bad that may get to sneak into one of your tanks.
Hose it out, wipe it down with a bleach solution, then Prime it over and over again to be sure the bleach is gone. That should fix it. I cannot stress enough---be sure to get rid of all the residue.
If bleach scares you, use straight hydrogen peroxide on a cloth. It's about as effective as bleach and the residue is not harmful once diluted sufficiently in water.
I had the same problem years ago. I found some small mold spots on the inside of my cover. The condensation would leak back into the can with no visible results but the water and plastic would smell. Cleaned with bleach rinsed and refilled with no issues. To this day I will still bleach can once in awhile. You never know what unseen contaminates may enter . Good cleaning once in awhile never hurts.