SnowyMoon ( cool nic btw )
I know exactly what you're talking about.
I had the 18' donut pool for two summers...
After I drained it the first summer, holy funk batman! WHEW & PHEW!
- mere words simply can not describe just how disgusting that rotton grass smell can become ( especially in the heat of summer, when I drained the first time)... it smells worse than dead skunk!
I swear we attracted every fly in a 5 kms area!
My neighbourhood stunk; it was embarrassing to hear the neighbours complain about the smell ( although they didn't know what it was or where it was comming from).
After that I had an excavation company come & remove the dead ground ( the smell actually sank a few inches down as well) & flatten/level the area out & then put some small-stoned gravel down.

I think that bleech will probably work fine for getting the mud/smell off. I used vinyl pool cleaner in a spray bottle. sprayed it on & left it there for a couple of hours before hosing it off & then letting it dry ( as best as I could; its so difficult because of the shape of these pools, it's practically impossible to dry the whole thing with all the folds in them)
If you have a pressure sprayer, this will take some of the work out of cleaning it.

You will probably need a new ground sheet.
I also bought a few smaller sized tarps ( because you can get a cheepo ten foot tarp here for about $10). Then I rolled up the pool like a burito for storage, using bungee cords to keep it completely closed.
The 1st winter, I left it outside in burrito state in the snow, it was fine the next summer ( no holes or apparent damages). the 2nd winter I wrapped it up & put it in the shed... I assume it waas okay since it weathered the 1st winter so well, but I sold that pool with my house, so I can't say for sure.

Anyway, hope something from my experience with this helps you,
Best of Luck to you & here's hoping that stentch goes away quickly