any pointers on how to remove 30 plus old goo from the inside of a fuel tank? it's pretty nasty lookin fuel coming out of there.

Depends on how big of a hurry you are to get it cleaned. I just got done doing one on a 75 F350 that had sit for 19 years with fuel in it. Was about 1/8 inch thick or more build up on the walls of the tank. I cleaned it using electrolysis. Pretty simple actually, use a 12 volt battery or a battery charger or both. Connect the negative lead to the tank, get a clean metal rod and suspend it inside the tank and do not allow it to touch the tank. Put in 2 cups of washing soda and fill the tank with water. With the battery connected the current flow will break the hold the rust and varnish has on the walls of the tank. On the tank I just done I changed the water out 3 times and after time #2 and 3 I pressure washed it with a high pressure hot water machine. The tank came out clean and an inspection with a light did not show any build up left on the walls. The box of washing soda was under $4.00 from the store. Just be sure to connect the battery correctly and there is really nothing caustic or harsh that your putting into the tank so I just dumped the used water on the drive way. This is the second tank I have cleaned using this process and have been happy both times. Do a google search and it will tell you more about cleaning parts this way. This is not fast but it is a inexpensive way to do it. Good luck to you.

I think this last tank it took about 2 weeks to do. I did not realize that I had run the battery dead though so not much progress was being made at that point! It is not a fast process but I am 40 miles from the radiator shop, I farm and this is the time of year that I harvest the crops and take them off the fields so I did not have time to go to town anyway. If your in a hurry then the radiator shop would be the best choice.

I'm running the stock tank on my 72, no sludge evident in my clear fuel filter. Bi-monthly doses of Sea-foam (catch it on sale and buy a couple at a time is what I do). Has also corrected non-functional fuel gauges in at least 2 cars, passed emissions in several others, and makes it where I don't have to drain my small engines for winter storage and they start up like new every spring.

For horrible sludge like ya'll are talking...Seal, add a can, fill it up, and let it sit. If nothing else, your radiator/gas tank shop won't charge you as much.

Good stuff, if expensive. You can catch it on sale for $6.99 a can at Schucks/O'reilly regularly.

Cheaper than the zinc oil additive I hope every one here with a non-roller cam is running.