Water heater: Replacing the dip tube. The wh-a-a-at?

I've had my Kenmore Powermiser 12 electric water heater since 2004. Lately, my hot showers went from hot to a cool version of warm. After checking the internet, I learned how to assess the heating elements and the thermostats; all tested OK. I adjusted the thermostats to make the water hotter, with no improvement. Additional research uncovered a detail of water heaters that few people know of. 

Hot water flows from a pipe at the top of the water heater. The cold water supply attaches to the top of the water heater. But the cold water doesn't stop at the top of the water heater. Water heaters have a tube attached to the cold water pipe at the top and run down to the bottom half or third of the water heater to make the cold water bypass the water at the middle and the top. This is the dip tube.  It keeps the cold water from chilling the hot water that's about to flow to your shower, tubs and sinks. If the dip tube breaks or cracks, cold water will mix with the hot water at the top of the tank and result in tepid showers.

I ordered a dip tube from Amazon. It was a 54" long 3/4" diameter tube with a flare at one end.  Home Depot had a dip tube with a 2.5" long 3/4" threaded tube attached--I ordered that, too, because I wanted to have one part that fit. 

I turned off the power to the water heater and turned off the water going into the heater. Next, I removed the flexible water supply pipe and the 3/4" pipe (this 5" long pipe with threads on both ends is called a nipple) that connected it to the water heater. The dip tube, or what remained of it, would be below that. Looking down into the hole from which I removed the nipple, I saw a mangled rubber/plastic washer, which came out with slight effort. I poked around below that with a thin long rod and felt nothing; the old dip tube had broken off and was sitting in the tank somewhere. The dip tube from Amazon wouldn't go down that hole. Just below the threads of that hole was some kind of fitting with an opening just slightly smaller than the outside of the dip tube. I widened that opening with a a round file until it was large enough for me to slide the dip tube through it. I cut the dip tube to fit inside the water heater so that the bottom end would be at about the level of the lower heating element. 

When I bought the water heater, the hype said that its coiled dip tube would make incoming cold water stir up the sediment on the bottom and prolong its life. I flushed a gallon of water out of the heater and saw very little sediment. The coiled dip tube worked, but I couldn't find one online and the local Sears store had closed. Installing a straight dip tube will obligate me to flush the tank annually.