Etymology

Supposedly from Hiram Codd, a British manufacturer of soft drinks, who patented several designs for mineral water bottles in the 1870s + wallop, a beer drinker’s pejorative reference to soft drink.
There is an absence of evidence supporting this. The suggestion is further discredited by early spellings of the term. OED Online-BBC Balderdash and Piffle

There is another possible source for this phrase coming from a connection to cod fishing. The long history of Cod Fishing in the North Atlantic as well as the earlier references to the phrase lends credence to its having an etymology dating back before the 1870's. The term wallop can mean the eggs (roe) of the fish, which in the case of the Cod fish was considered useless garbage as compared to the value of such items as caviar. This explanation gives an even closer etymological definition for the current use of the term as meaning something that is of little or no value.

Evidently by folk-etymology referring to swill, this word has North American variants hogswallop, hog's wallop, and hog swallop.

Noun

1. senseless talk or writing; nonsense.