  Tau lepton emission in two-nucleon disappearance reactions from within nuclei
which conserve baryon number minus lepton number (B-L) is considered. It is
shown that some existing limits on proton decay channels and two-nucleon
disappearance reactions resulting in electrons and muons can be applied to
$\Delta B=\Delta L=2$ decays involving $\tau$ leptons. For the two-nucleon
disappearance channel $np\to\tau^+ \overline\nu_\tau$ the estimated limit for
the partial mean life is $\frac{\tau}{Br}>1\times10^{30}$ yrs based on results
from the IMB3 experiment. Re-analysis of existing data and future experiments
could result in higher sensitivity for two-nucleon disappearance modes
involving $\tau$ lepton final states.
