A load of codswallop
The origin of the term 'codswallop' is unclear. The most widely quoted story is 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 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, but there's no actual evidence for that derivation. In fact, such neat plausibility without evidence is often the mark of the linguistic mythology known as folk etymology. Look no further than these popular fallacies for confirmation.
The earliest known citation of the phrase in print is in the script of a 1959 episode of the UK television series 'Hancock's Half Hour'. The writers Galton and Simpson don't claim to have coined the phrase, which they say was in public circulation when the show was broadcast.
'A load of codswallop' sounds old and the Hiram Codd story has a certain appeal. The problem with the tale, apart from the lack of any supporting evidence, is the entirely implausible notion that the phrase was in popular circulation since 1870 but somehow didn't manage to get into print until 1959. That lack of printed record is despite the fact that an appeal for early citations made on national television in the UK in 2006 failed to uncover any earlier than 1959. Also, if Mr. Codd's drink were the derivation, we would expect to find early examples of the name in the form Codd's Wallop, but there aren't any such examples. That, along with the fact that the term 'wallop' itself wasn't associated with its 'drink/beer' meaning until well after Codd's death, makes the 'Codd's Wallop' derivation highly improbable.
The most likely explanation is that it is a made-up nonsense word that just sounds right for its meaning.
'Cod' is a little-used slang word meaning 'to hoax or take a rise out of', known since at least 1873. It was used in much the same way we now use the verb 'to kid', as here in a quotation from 1884:
"Tha'st only coddin me as tha allus does; tha'l none tay me to see th' fair."
That could be the origin of the cod in 'codswallop', but this is just plausible speculation, which brings us back full circle.