If the obstruction was RUST then are we talking an obstruction in a short stub of pipe or a nipple or the house plumbing? Is the pipe galvanized or copper?

The latest Raleigh, NC water quality report dated 12/2011 http://www.raleighnc.gov/content/PubUtilAdmin/Documents/WaterQualityReports/2011/Finished_Water_Quality_Report_1211.pdf

It reports 2gpg hardness with a touch of iron and manganese but a constant PH of 8.4 which is high. High or low PH can damage pipes and should be corrected.

I'd hit the Yellow Pages and call an independent water treatment pro and get a free quote to at least correct the PH and maybe a softener for the hardness, iron, and manganese.. A competent water treatment pro should be familiar with the Raleigh water and know the PH is 8.4

Thanks for your reply. The pipe is copper but not sure what the nipple is. It's silver colored. No rust on the outside. Heater was flushed. Would replacing the anodes help? It's a 50 gal gas Rudd/guardsman. Looks like possibly both an aluminum and magnesium rods.

If the rust was only in the nipple and not in the copper then most likely a galvanized nipple and they rust... especially when the PH of the water is not right.

I'd also replace the galvanized nipple with a brass nipple if the code allows.

Annual drain and flush of the WH is a good idea.

As I said "I'd hit the Yellow Pages and call an independent water treatment pro and get a free quote to at least correct the PH and maybe a softener for the hardness, iron, and manganese". I prefer to cure the disease rather than just treat the symptom.