Bathroom fan dripping back

After showers the condensation in the duct from my bathroom fan drips back into the room.

I have a fan timer and we've been running it for 30-45 minutes after showers. The fan is old with a regular bladed fan (not one of those squirrel cages). The duct is PVC pipe running horizontal along the attic floor for about 10 feet until it turns up to go to the roof vent.

Any suggestions?

Insulate the ducting or hose if you can all the way to the exit point.
The duct can also be rerouted or replaced so that it slants to the exit point so any condensation goes outside.

There have been some good discussions on this at Greenbuildingadvisor

If this is a new development, make sure the venting isn't plugged with lint, dust, or insects.

Seriously, buy some 4" insulated flex duct.

http://www.amazon.com/LL-Building-F6IFD4X300-Insulated-Duct/dp/B0026SM4CG/ref=pd_cp_hi_1

Replace the unit with a ducted fan for silent operation while you're up there.

I like the insulated flex duct and use it. The steamy air that you are trying to remove from your bathroom is cooling on its travels through your attic, condensing, and running downhill back into the room. The idea is to keep the travel path warm enough that the bathroom air exhausts before cooling enough to condense. Basicly, your flue temps are too low and you're getting creosote. Use a short, direct, insulated path from fan housing to the outlet.

I like a noisy bathroom fan. Women especially seem to like the cover noise. I don't need to hear the deuce splashing down or the noises of an ill person in the bathroom. There is a certain pride I take in being able to overpower the noisy fan with a particularly sharp flatulence from the shower stall

You might also check the discharge vent itself to make sure that it is closing completly when the fan is off.

My son had same problem. We checked in attic and discovered flex duct pipe had a bend in it providing a place for some of the moist air to turn into water and running back down the duct to the fan. We straightened the pipe out so air had a clear escape path, and problem was solved.