I got my gas tank off e-bay and the inside was really rusty. I talk to my local stealership and they sold me a three part cleaner and said it was easy and just follow directions. I started this on sunday by cleaning the tank per directions with soap and water, then took part A cleaner mixed with water and let it set until today to make sure it was really clean and then did the next two steps today. now I just need to let dry for the next 24 hours. this was not bad to do.

not to rain on your parade, but gasoline, and rocks or nuts, and shake and drain works just fine too!  Just splice in a clear inline fuel filter and replace as needed!

as suggested be sure and install and inline filter - you can pickup a small see thru with replaceable filters at the local auto store - be real good insurance in case the sticky part misses some of the rust

1/4" is correct, I believe.  You can always pop it off when you get to the parts store!  If the fuel lien has already been replaced, it may be labelled on the side.