* When toilet was off, 2 gal buckets of water poured down drain as fast as
possible went down without problems or backing up.

This tells me that the toilet's integral trap is clogged. You are unable to
see fully into the integral trap of a toilet. Get a closet auger and clear
the clog. HD and Lowes sell them. It should look like this:
http://www.drainbrain.com/rental/closet.html

Here is a link to a cutaway diagram of a toilet.
http://www.toiletology.com/anatomy.shtml

Page down to the "common bowl types" and look how the front part of the
integral trap of toilet is hidden unless you stick your head down into the
bowl. Don't stick your head down in the bowl, ask and I'll send over my
brother-in-law to do it for you--no charge.

Al