Is there an idiom for "I'm not an expert when it comes to kinds of feces"

There is an idiom in my language, which literally sounds like "I'm not an expert when it comes to kinds of feces". Which means that one considers all the instances of some group as equally bad, not to make an opinion about any (for example, politicians). Is there an exact equivalent in English for it?

The original version is in Ukrainian. It is "В сортах гівна не розуміюся". In Russian it is "В сортах говна не разбираюсь". It's a relatively young, but very common expression.

LET GOD SORT THEM OUT

The OP has stated that the phrase in question, "means that one considers all the instances of some group as equally bad ... "

The meaning of the OP's phrase is about not caring, as opposed to, not knowing. Additionally of great significance, the phrase is an expression of vituperation and disdain, conveying a fundamental lack of concern or moral consideration for any who fall within this category (choose your favorite 'scapegoat') because these have been judged to be the equivalent of "feces," and there are no "grades" of feces, each and all are merely and only, "shit."

While admittedly not an exact equivalent, there is a phrase which pithily sums up the same blithe lack of moral concern and invective, “Kill them all; let God sort them out." This phrase is considered to be a derivation of "Caedite eos. Novit enim Dominus qui sunt eius", a phrase allegedly spoken by the Papal legate and Cistercian abbot Arnaud Amalric, prior to the Massacre at Béziers, a massacre in the French town of Béziers that formed the first major military action of the Albigensian Crusade. A direct translation of the Latin phrase would be "Kill them. For the Lord knows those that are His own." See, Wikipedia Caedite eos. Novit enim Dominus qui sunt eius. The phrase was possibly a misunderstood reference to 2 Tim. 2:19 which, in part, reads, “The Lord knoweth them that are his”.

To minimize the distinction we say, One's as bad as the other:

Or, if we leave room for more than two:

One's as bad as the next.

An exact match:

I don't know shit about shit!

From The Slangman Guide to Dirty English: Dangerous Expressions Americans Use., by David Burke:

"I don't know shit about shit, but I know right from wrong!"

From An Uprising of Angels, by Marc D. Baldwin:

“I don't know shit about shit. Okay?

From Four-letter Films: Taboo Language in Movies, by Gabriele Azzaro:

Look, I admit I don't know shit about shit.

In all of the above references, the meaning of the phrase is roughly: I know very little about [things] that are worthless to me, which is derived by combining the meaning of the slang phrase don't know shit and the slang shit.

The slang shit refers to, among other things, a worthless person or thing:

From Oxford Dictionaries Online

noun ...

2.0 A contemptible or worthless person.

3.0 Something worthless; garbage; nonsense:

The common slang expression: not know shit, builds off of the meaning of shit, and means that the subject knows nothing:

From Oxford Dictionaries Online

Not know anything.

If someone says: I don't know shit about politicians, they are implying that they know [or care] extremely little about politicians. When someone says: I don't know shit about shit, they double down on the contempt, by implying that the matter at hand is worthless, and they know [or care] very little about it.

Not wishing to double down on a taboo, one might choose a slightly more formal,
I don't give a shit:

(about someone/something)

tv. to care about someone or something. (Usually objectionable. Often negative.)

I don't give a shit about politicians! This approaches the exact match, because people who don't give a shit about shit, don't know shit about shit.

Many diminish the taboo (and contempt) by replacing the word shit with:

• damn
• hoot
• hang
• rip

Adding the word flying into the expression seems to increase the sense of antipathy.
I don't give a flying:

• f#@&
• fig
• shit
• fart
• leap
• flip
• hoot

It's all the same to me:

something that you say when it is not important to you what happens

Billy Ray Cyrus wrote It's all the Same To Me about a bad experience in love, where all the gory details became irrelevant:

Refrain:
You can put me on some island In the middle of the sea
Or lock me in a prison With no chance of ever being free
Or run a dagger through my heart Stand back and watch me bleed
Oh, baby you can leave, It's all the same to me...

Without you, It's all the same to me

I could never love someone else
If I can't have you You might as well leave
Yeah baby if you leave It's all the same to me