If you want to drain the bar sink into the bathroom drain, if can
only be a few feet away or you might have to vent it too.

They do make a venting piece that doesnt require you to
vent it outside. (I forgot the name of the unit, but its
real popular to use when installing a sink into an island
in a kitchen.)

Only catch about that piece is that you need to have access to
it because the rubber flapper needs to be changed every few years for
proper use.