Noodle, wow. He's 3 years old and he's spent it all at a pet store? That's kind of . . . lousy store.
Well, since he's never had clean, conditioned water the first thing you'll want to do is acclimate him very carefully. I'd suggest using the drip method. 2 ways to do it.
1) Get a length of airline hose. Put the fish in a container with the water he was bagged in. Put one end of the hose into the tank that will be his new home and get a siphon going. Tie a knot in the hose until the flow is just a drip into his temporary container. Leave him like that, with the new water dripping gradually into his container, for about an hour. By then, the water should've doubled or so in volume and he should be sufficiently used to it to go into his new home.
2) If you don't have an airline hose, then every few minutes you can dribble about a tablespoon worth of new tank water into his temporary container. Do this until the water has doubled in volume. Then he should be ready to go.
After he's been in clean water (tannin stained is okay) for a day, get him started on his meds. General Cure and possibly add Kanaplex too. If he's really in bad condition, add 1 tsp of epsom salt per gallon too.
Now, since this guy has been in pretty bad conditions there's a possibility he's a carrier of a whole bunch of diseases and bugs so be very careful to not cross-contaminate anything with Tony.
I hope the big guy lasts until Monday. Even if he doesn't make it, it would be nice if he could spend at least one day in clean water with someone who cares.