My ES-P's drain simply goes directly to a scrap piece of aluminum tubing (~1/8" ID) potted through the bottom of the fuselage.  Works great so far.  There's always air exhausting the cabin anyway.

One thing i learned the hard way:  the A/C inlet vent in the rear, while located just right to allow airflow over the rear evaporator, is also located just right to let rainwater in!

-isaac heizer
N7842K