What are the connotations of "u'S'hi Nidasah alav"?
Rashi: It means that, like the Nidah herself, the man (is an Av ha'Tum'ah, and) renders Tamei Adam and K'lei Cheres.
What does the latter half of the Pasuk, which is seemingly superfluous, teach us?
Rashi (in Yoma, 6b) and Rashbam: It teaches us that, although the Mishkav of the Nidah herself is Metamei Adam v'Keilim, the Mishkav of the Bo'el Nidah is only Metamei food and drink. 1
Rashbam (citing Nidah, 32b):What is underneath a Bo'el Nidah (Mishkav) has the same law as a Kli over [and touching] a Zav (a Rishon l'Tum'ah),
Why does it say the double expression "Shachov Yishkav"?
Moshav Zekenim: This includes Bi'ah k'Darkah and Lo k'Darkah.