never assume anything
a drop rate of 1/4" per foot
so 20' 5" drop
As for the vent use a Air Admittance Valve
http://www.studor.com/index.htm

DL wrote:
I would like to install a sink in our garage. Running the hot / cold
won't be a problem other than precautions I might need to take to
prevent freezing lines in the winter months. As we keep our rabbit
in the garage during the winter, I assume it doesn't get cold enough
to freeze the lines. Anything I should be concerned about?

Based on where I can gain access, the drain line will be approximately
12-15' before it taps into a vertical drain connection. I would plan
enought slope to ensure proper drainage. Seems to me that whether it
be 1' or 20', it should be fine as long as the slope ensures proper
drainage. Is this too far?

My biggest concern is the venting for the sink. Will a sink drain
properly if the venting is run from the where the garage sink drain
line connects to the vertical drain line. My assumption is that it
will and should be that way. I have to confirm it the vertical line
is or isn't a vent line as well. If the vertical line doesn't have a
vent connected to it, I would tap a connection to another vent line
just above / before where the garage sink drain connects to the
vertical drain line. Concerns / recommendations?

My other option (not really preferred) is to run a vent from just
after the trap before the drain line goes through the wall into the
basement area to be surface mounted do that it exits the garage and
then goes above the roof line somehow. I am not sure this will work
effectively if the vertical connection is 15' away, plus it will be a
hassle getting the line to exit above the roof line.

Any comments or recommendations would be greatly appreciated.

David