1)
Why does it say "El ha'Amudim"?
1.
Radak #1: This is like Al ha'Amudim.
2.
Radak #2: El means for on behalf of, like "va'Yomer Avraham El Sarah Ishto" (Bereishis 20:2).
2)
What are "ha'Mechonos"?
1.
Rashi citing Targum Yonasan: They are the bases [of the lavers]. This is like "Es ha'Kiyor v'Es Kano" (Shemos 35:16).
