As slang, 'a crock of shit' is similar to 'a white lie'.
It's poetic metaphor: consider that a
crock pot cooks food slowly but thoroughly, which has advantages above just
tenderizing. For example, before refrigeration, people had to more frequently encounter meat that may have been starting to spoil, and had to do something to make use of it. They would do what they could to kill off the bacteria as best as possible, perpetuating the popularity of
slow cooking. Soups are sometimes good for this too, since the bacteria has a better chance of dying off with meat cooked through and through.
The coorelation here is in the exaggeration that implies that a crock of shit should be harmless, if the bacteria is eliminated. The truth is that even food that is too rancid, even when cooked thoroughly, is still bad for you. Kill off the bacteria in a pile of shit and it's still nonedible. Comparing deception to shit, sometimes people try to justify their behavior while claiming that they are also
mitigating the side effects. Sometimes they get called out by someone else as its being a crock of shit. Simply put, with the context this is usually used with, no matter how it's prepared, scandal is probably bad for you.
* Supposedly, modern
sewage treatment is a different idea altogether.
