Meaning:
Lit. “the bottom and ten meters of sludge”. If you hear this have no doubt that your interlocutor is of an extremely negative opinion about somebody’s behaviour, a book, a music album or whatever else. Be sure to only use it if you really cannot find any positive aspects of the subjects of your conversation. Any proponents of what you’re criticizing this way will feel provoked to start an argument with you and await some brilliant points to support your judgment.
Pointing at something displeasing as “dno” (the bottom, of a sea, lake or a river) has been used in Polish for several decades while the level of sludge seems to be an addition of the recent twenty years in the era of Internets and everybody voicing their opinions about everything online. Several variants exist.