A bucket, 1 gallon of white vinegar, a small submersible "floor sucker" in a bucket, 2 washing machine hoses and hopefully he has the service port valves with flushing hose bib attachments that allows you to isolate heater from water supply while pumping solution through heater while it is off.

Why are you flushing? Did he record the rise through the exchanger when new and it has increased 3-5 degrees since new? All this is available on a quality heater with the remote control.

We are on well water and his shower walls are white with calcium deposits. I thought you were suppose to flush it every 6 months. We did not record any readings when it was installed. Our plumber never mentioned it.

"We are on well water and his shower walls are white with calcium deposits."

Sounds like the calcium is coming out of solution but not sticking in the heater.

There are any number of cleaners to remove calcium deposits.