What's the English equivalent for the Italian slang expression "magna magna"

"Magna magna" is a typical Italian slang expression commonly used by people to give vent to their frustrations and disappointment with politicians when cases of corruption and personal interest in public affairs are brought to light.

Literally the meaning is "eat eat", where the verb "eat" in this case is synonymous with "steal". The common saying is "e' tutto un magna magna" that is "it is all just a magna magna".

I can't find a reference on this subject.

What are the equivalent BrE and AmE (possibly slang) expressions?

Quite similar is

have/get one's nose/snout in the trough

British disapproving

to be in or get into a situation in which one is getting or trying to get a lot of money

{Merriam-Webster}

'He's got his nose in the trough' could be applied to any person over-eagerly procuring money, but is almost always used for illegal or at least dodgy practices.

Oink oink might be closest in form in American English. This is the English word for the sound a pig makes, and can be used to mean "greedy" (similarly to the trough idiom, I think). "Oink out", for example, equates to "pig out", meaning overeat or binge (see, for example, The Free Dictionary), and I might say "oink oink" as a humorous admonition to my child if I saw him reaching for yet another donut.

Helpfully for this situation, in the US "oink" also evokes political "pork"¹. "Pork barrel" is an idiom for a particular kind of political corruption:

pork barrel: government projects or appropriations yielding rich patronage benefits (Merriam Webster)

pork 2: government funds, jobs, or favors distributed by politicians to gain political advantage (Merriam Webster)

This usage of "oink" is not as widespread as the Italian saying you describe, but I think would be pretty instantly understood in context. Some examples from around the web:

(By Jay Lassiter)

(Article at 100% Fed Up)

If, for example, the highest executives of the nation or of the state are called, not President X or Governor Y but pig X or pig Y, and if what they say in campaign speeches is rendered as "oink, oink," this offensive designation is used to deprive them of the aura of public servants or leaders who have only the common interest in mind. They are "redefined" as that which they really are in the minds of the radicals. (Political Humor: From Aristophanes to Sam Ervin By Charles E. Schutz, 1977)

¹Note that "pig" is also a derogatory term for police, and "oink" can be used to reference police (especially those who abuse their powers), so be sure of your contextual cues when/if using.

The idiom to feather one's (own) nest fits the bill which means:

(figuratively) to use power and prestige to provide for oneself selfishly. (Said especially of politicians who use their offices to make money for themselves.): 'The mayor seemed to be helping people, but she was really feathering her own nest.' 'The building contractor used a lot of public money to feather his nest."

[McGraw-Hill Dictionary of American Idioms and Phrasal Verbs]