The reflexive pronoun for the second person (informal) is te, not tu. So it would be tu te connais.
The plural pronouns are necessarily more ambiguous because they can mean "each other" or "one another".
Hence the need for both the reflexive pronoun (vous/nous se) and the "nous/vous/eux/elles-mêmes" versions.
In addition, even the formal singular "vous" needs the same fix if the context is not crystal clear.