Well you cant seal the tank, or you'll create a vaccum, so need a S bend in a breather pipe. (Like at home). Think you will need much more capacity than a pint or two. You need more capacity than the pipe work for a start or it will just pump it half way up and stop, then it will all run back again. Think about it!! Can you not just send sink and shower water straight over the side. Mine dose. My holding tank would be full about three times a day if sinks and shower run in to it as well.

Haydn