Thanks all,
I am going to go with a liner. As you guys suspected I do have more than just the 2 pin holes. Its more like 4 from what i can tell, though the metal seems pretty solid. Couple of things I learned doing this. And unfortunately didn't really have a great solution to either but just thought I'd share. Maybe someone else my think of a better way before getting knee deep in the middle.
- The 550 tank doesn't have any opening at the lowest point of the tank. Meaning, flip the tank upside down and the counter sink of the tank cap area becomes a raised platform. And right side up, the petcock area apparently isn't the lowest point as I couldn't get everything to drain. I have shaken the hell out of the tank today and it took forever to get the vinegar and then the water out of the stupid thing. I did use alcohol to dry the remaining dampness. Because I didn't have my liner yet, I just poured in container of Marvel's, then shook it, and have left it in. I did use air from a pump for the alcohol, but didn't have access to a compressor to hit with high pressure.
- Sheetrock screws Vs BBs as a shaker media. As most know, one of the recommendations is to fill the tank with a pound of screws or something to rattle around for a while in the tank to dislodge the loose rust. I chose BBs. They sounded like a better idea because they are smaller. Could get to more areas right? Well they did a great job but for the reasons listed above, they were a pain to get out of the tank. It's up to the individual, but for a tank with a counter sink cap I would strongly recommend something larger than BBs. Something you can reach in and get the last few by hand.
I have come to respect the guys that went through this process on a painted tank. I had rust filled vinegar and then water all over everything. In any case I really do appreciate all the good info. Now to find where I can get the liner. Advanced Auto here didn't have it.
Thanks
Ace