Salty dog as far as shocking your tank. You only need to do it when you need to so I wouldn't say it has to be done regularly. Yearly might be more than enough. As long as there isn't light getting into the tank it will stay clean along time. The chlorine in city water will allow it to stay fresh quite long. It might start to taste funny
long before it is unsafe. Just flushing
with City water will do a lot.
When you do shock it you are killing a few germs not making it clean inside. The municipal drinking water
system uses Chlorine and you don't generally smell or tastes it at that level (OK some folks can). So the basic rule
is once you can begin to smell it coming out of the faucet it's enough. I used to have the concentration written down but just a guess from memory would indicate maybe 8 ounces for 170 gallons.
Add the bleach then dilute to fill the whole tank. Turn on everything until you can smell it coming out of all outlets. Come back the next day and drain the tank 100%. Next maybe add 20 gallons and pump that out repeating until the taste is gone and if you really want to fill and drain one more time and it should be done. The goal is to kill not to "clean".
and lines can accrue mineral deposits that can harbor elements that can alter the taste. To get rid of that takes strong chemicals and that process is far more complex unless you don't mind drinking toxic chemicals. Putting them in is easier than neutralizing them and cleaning
them out as well as the sediments they create. Opening up the tank is really the only way when it gets that bad.
If you dumped down a gallon or two of bleach it would start to degrade the system, but I doubt it would destroy it. If my guess was totally wrong the right number might be 16 ounces but clearly no more and maybe less. More added really won't kill them "more dead".
I just installed a belt drive pump and then set about winterizing the water system. Never drank a drop from it yet. I can tell you how great it is in late March or April. They cost about double under $400. The pump head
is much like a March circulating pump I use on the A/C system. It means you can disassemble the pump head
and do things to it. You can also just buy a spare head.