Welcome, careless.
I had a foreclosure swamp, black, that I recovered using the TFP way. I had water table issues and a vinyl liner, so recovery as opposed to draining was the route I went.
However, once you post back the pool type and any pics of equipment filter type, etc., I may be able to help you assess the quickest strategy. Here's some starter info.
Approach #1 - Using TFP SLAM (read up in pool school) Hand rake all debris blind from bottom, wearing gloves and maybe mask (I had added 5 gal chlorine before starting this just to try to knock down any pathogens, but the ammonia likely ate that chlorine immediately...)
If black, its likely your cya will have turned to ammonia. Get an ammonia kit from fish store to read. You will initially need to keep adding chlorine, eg every half hour, until you've broken down the ammonia and the water starts to hold the chlorine for more than an hour. You will need to babysit the pump basket for clogs and backwash very frequently for the first few days...every time pressure is 25% above normal.
If you have a main drain, it will help to keep that valve partly closed when first filtering to avoid clogs. You will not be able to use a system pool vac (manual) for a while. After start up, proceed with slam but be extra vigilant never to let chlorine level drop belw high end of slam rate, whch is based on cya ratio.
Pros: This works, but is bit labor intensive and requires at least a free schedule for the first few days. In Our case, hauled 20 wheelbarrows of crud. Breaking down the ammonia makes it difficult to get started on slam.
Approach #2 - Trash Pump, partial refil, then Slam. In this approach, you rent a Heavy duty trash pump, set it on bottom, and pump off water and sludge from bottom. If vinyl liner, do not pump lower than a foot in shallow end. Monitor the pump because we have seen an odd case where force of pump has ripped liner.
For any other surface than vinyl and IF your water table is solid (note: fiberglass shells can pop) you could continue pumping, then clean surface, refill, balance chemicals and then SLam to remove algae and pathogens from pipes etc. it will be a much shorter slam.
Pros: Faster recovery, less labor, and a bit less chlorine to recover because your concentration of ammonia would be diluted, as is the degree of other crud, ergo slam goes faster.
Approach 2.5 - Sheet Method for High Water Table or alternate for Vinyl on Approach #2:
In any surface with a high water table, or water table is unknown, or vinyl for full water change, you can use method 2 and add a taped sheet of visqueen (available in boxes at hardware store) over the surface of the old water that's getting pumped. Add freshwater simultaneously on top of the plastic sheet to keep clean water and sludgy stuff separate. When refilled, remove the sheet. You will have mostly clean water that will be easy to quickly balance and Slam.
Hope this gives you some ideas...but let us know your specifics, and be sure to read up on two important concepts here: the cya:FC ratio and how to slam
You will love your troublefreepool pool one day, I promise!
Here's the pictographs of my recovery:
