An often quoted source in favor of metzitza b’peh is the Binyan Tzion siman 23. However, there doesn’t seem to be anything in there that would be against metzitza with a tube provided that it does as good of a job at drawing out the blood as metzitza b’peh would do.
R’ Moshe writes that it’s pashut that metzitza is not meakev the mitzvah.
Igros Moshe Y.D. 1:223:
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