Help!! Clogged Basement Drain

Ok here's the deal, it looks like I've completely screwed up the drain in my utility sink in the basement. I'm pretty sure it was caused by the unfiltered output from my washing machine in combination with the gravel and sand from me periodically cleaning my 120 gallon aquarium. The problem is also compounded by having old rusting cast iron pipes. So far I tried to disconnect the sink and snake the drain but I was unable to push the snake in very far. I then tried to gain access via the cleanout but the plug is stuck on pretty damn tight. I went to work on it with a wrench and hammer but it simply wouldn't budge. I've attached a few pics to illustrate the problem. The other drains in my home are working fine, I haven't noticed any slow down so far. Any advice on how I should handle the problem?? I'd prefer not to call a plumber unless absolutely necessary....Thanks in advance!!

Cut out a section of that old Galvi pipe. Snake the drain. Then replace old section with some new pipe. Try to make sure you use Missions bads to connect new to old.

Most likely that the cleanout cap is fused into the tee, but you can give it one last try by heating the fitting nicely and then trying to tap it loose a bit with the hammer, and then see if you can get it to move with a wrench at all. I doubt it will work, but it's worth a shot. If not, then patrick88's suggestion is about all you can do without calling in a drain cleaner.

You might try soaking the plug with PB Blaster. That's about the best penetrating oil there is. Note: WD-40 is not a penetrating oil as many people think. Give it several sprays and let it work for awhile. Tapping may also help. You then will need a good wrench that fits the plug really well and a cheater bar on the wrench.