Tank Rush is an old Aggie tradition that is no longer practiced, probably because it would be considered hazing today.
The idea was simple. Round up all freshmen on campus, and make sure they were dunked in the nearest body of water: either a tank for the farm animals, drinking water tanks, or Putah Creek. This would be coordinated by all the upper classmen, who would spring it on Freshmen randomly during the Fall semester.
This was practiced throughout the 1920s and 1930s and probably longer.
This tradition was written about in the October 6th, 1915 edition of The Weekly Agricola.
The 1916 Annual Tank Rush was filmed by two moving picture firms and seems to have had a set time limit and a specific concrete irrigation pond. There were 140 seniors and 140 "Freshies". At the end of the thirty minutes there were 40 seniors left on the field.