Water Heaters - exhaust for a gas water heater

I have a question concerning the exhaust running off of my gas water heater at my home. The exhaust pipe coming off the top of the water heater goes into a larger exhaust pipe. Right below where the exhaust connects to the main is what looks like a small canister. This canister is the bottom of the larger exhaust pipe. It still has a product name on it, it is a 5" plug small end. This canister appears to be filled with a powdery substance. Should that canister be cleaned out?

I would like to see a picture ( try www.photobucket.com) of what you are talking about. It sounds like rust and corrosion flaking off the inside of the pipes. It should be cleaned out, but may be a symtom of some pipes which should be replaced.

Is this vent pipe a gas B vent pipe? How is the draft at the water heater vent hood good?

594tough

I've posted the picture of the canister. It can be seen at the following:

http://i140.photobucket.com/albums/r4/forginoe/exhaustpipe.jpg

Thanks for the help. John

How is the draft at the water heater vent hood good?
If so It all looks good to me. Might check the top cap of the flue up on the roof and see that it is ok .