Okay, here we go...
Make sure you get a GOOD test kit with LOTS of reagent refills.
First we start with a little bleach...
Well maybe a machete, a weed whacker, and a LARGE dumpster.
Then you are going to need to get a pool rake and make sure you get as much stuff off the bottom as you can. Keep trying to get as much out as you can, even if you can't see bottom.
We'll be here when you are done with that. Shouldn't be more than a week or two...
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All joking aside, I would love to tackle this one. Given what I know now, I truly believe that since it still holds water, it is savable.