  We investigate the electron transport in multiply connected metallic carbon
nanotubes within the Landauer-B\"{u}ttiker formalism. Quasibound states coupled
to the incident $\pi^{*}$ states give rise to energy levels of different widths
depending on the coupling strength. In particular, donorlike states originating
from heptagonal rings are found to give a very narrow level. Interference
between broad and narrow levels produces Fano-type resonant backscattering as
well as resonant tunneling. Over a significantly wide energy range, almost
perfect suppression of the conduction of $\pi^{*}$ electrons occurs, which may
be regarded as filtering of particular electrons ($\pi$-pass filter).
