I don't want anyone telling me what toilet to use, but I now have several of these that flush great with 1.5 gallons of water. With the price of water these days, I'm happy.
http://www.terrylove.com/crtoilet.htm
the toilet is only part of the problem. Did you see the story about San Fran a few weeks ago that there is not enough water clearing out the “sludge” from the sewer lines and they are starting the have major problems with blockages? (ok, ok , insert your jokes here)