You want me to do *WHAT*?

Dad thinks the water is from the drain hose being blocked. He suggested I blow into the drain pipe:

(Uh... *how*?)

I decided to start at the other end:

See the U shaped trap? I disconnected the right side, and tried pouring water down. Water poured. Nothing seemed to be dripping out of the furnace side, though. *sigh* I reconnected the trap, cupped my hands around the outlet, kneeled down, and blew. I heard some gurgles, so I'm assuming I actually managed an okay seal. Fingers crossed that that worked. I'll check to see how the water looks in the morning.