This may have already even been suggested here, but I did it last night with happy results (I was reminded when I took a shower in a non-flooded tub today!) Pour about half a cup of baking soda into a clogged drain, then pour in about half a cup of vinegar. After it sits for 20 minutes or so (longer is probably fine, as it isn't as corrosive as something like Drain-O would be) flush. Voila! Bird-safe, non-toxic drain cleaning!