I find that a little splash of it behind each ear gets chicks - they get the urge to start nibblin'!
(But, Seriously) It depends on where you're located at the time of year:
WARM WEATHER:
Get a big funnel & save some gallon plastic milk jugs & lids. Pour the goop into the jugs through the funnel, seal-up tight, put into a plastic bag tied tight and put in the trash.
(If you have a garden, and only use the smoker occasionally, you could dig a trench & burry the slop, but it may attract undesired critters.)
COLD WEATHER:
Let the pan cool down. Grease will solidify & float on top. fish & scrape it out with tongs, bag, & discard. You can now dump the water down your waste disposal without much problem. (It's the grease that creates problems with plumbing / septic - if you separate the grease out, the rest of the crud is pretty much sewer-safe.)
Hope this helps