Word origin

[MRMKHS1]

ORIGIN OF "CODSWALLOP"?

[scotman]

Chambers gives the following source

thought to be from a bottle patented by Hiram Codd, the fizzy drink it contained being ridiculed as "Codd's wallop"

[DTCwordfan]

origin of the term codswallop is unclear. The most widely quoted story has it that of Hiram Codd, an English soft drinks maker during the 1870s, who developed a technique for bottling lemonade. This process involved the insertion of a glass marble as a stopper into the neck of the bottle. When the bottle was shaken the resulting pressure from the fizzy pop forced the marble against the neck to form a seal.

The device was called, not unreasonably, the Codd Bottle.

Wallop is a slang term for beer, and beer drinkers would certainly be disdainful of bottled soft drinks. This slang term dates from around the early to mid 20th century. Eric Partridge, in A Dictionary of Slang, claims it as serviceman's slang and dates it from the 1930s. An early example of it in print comes in J[ohn] B[oynton] Priestley's Three men in new suits, 1945:

"It's drink... Booze or wollop... Nine times out of ten... you wake up in the morning... with the usual hangover."

It's not difficult to see how a soft drink in a Codd Bottle could have come to be called codswallop.

[heathfield]

Codds patent was for a self-sealing soda water bottle. A weak beer, (wallop) would be described as 'Codds-wallop' to mean it was like drinking soda water. The description later became used to describe almost anything that could be considered rubbish, e.g. a statement.

[Quizmonster]

The scholars of The Oxford English Dictionary fail to give the various myths as to the origin of codswallop house-room. They say the origin is unknown, so unknown it is.
The main urban myth is that a Victorian businessman named Codd either made bad lemonade or a device for sealing lemonade bottles. The latter, supposedly, had to be forcibly pushed or walloped down into the bottle in order to get at the liquid...hence, ‘codswallop'! It's a lovely story, certainly, but almost certainly rubbish!
Actually, 'wallop' as a colloquial name for beer dates back only to the 1930s and there is no evidence that it was ever applied to lemonade. Its connection with liquid at all relates to the onomatopoeic effect, since the word sounds like rapidly boiling water.
One old meaning of ‘cod' was a bag or purse, vulgarly used to mean the scrotum, and thus 'cods' meant 'testicles'. That is a much more likely connection with the idea of nonsense. People may at one time have used cods in much the same way as we today use the b-word for those organs to mean 'nonsense', too.
In fact, 'codswallop' itself is not recorded anywhere prior to the 1960s, as it happens. Had it been around in Victorian times, as often claimed, I cannot imagine Dickens, say, would not have used it in the mouth of one of his London characters.
All-in-all, you can - as usual - safely discount any of the folk etymology sources suggested.

[beso]

A cod is certainly a reference to the scrotum or a bag such as a codpiece which is a part of the trousers covering the crotch.

Walloping is seems very similar to many euphemisms for m@sturbation.

Hence codswallop probably refers to information provided by what might be colloquially known as a w@nker.