Need to sanitize system if only using city water?

[Great Eggstrications]

For some trips we know that we will only be using city water hookups - never the fresh water tank and pump. Anyone have any thoughts about the necessity of sanitizing the fresh tank in such cases?

As I understand it, when hooked up to city water there is a check valve that keeps the city water from going into the fresh tank and out of the pump, and the water that shows up at the plumbing fixtures (faucets, showers, toilet) is exclusively from the city supply, not the fresh tank.

I don't particularly like going through the 'add bleach and flush the system, add bleach and flush the system again' routine, especially having done it more than once outside in the rain in Seattle. I typically store the trailer between trips with essentially a virtually empty fresh tank, and am hoping that for 'city water only' trips we can forgo the bleach sanitation drill.

Proposed procedure:

1 - Pump (or drain) old water out of the fresh tank and the water heater tank

2 - Get hooked up to the trip's first city water hook-up

3 - Open all cold faucets and expel the old water remaining in the cold plumbing lines (using city water pressure, not the pump)

4 - Open all hot faucets (2 sinks and outside shower) till water heater tank is filled up with new city water and the old water is expelled from the hot water lines (using city water pressure, not the pump)

One potential problem with this would be that there would be some old diluted gungy water left in the water heater tank. Maybe only use hot water for showers and washing - not for consumption? I recall that it's a numbers game when filtering water while backpacking - there will always be bad stuff in the water, it's just a matter of keeping the numbers low enough so your body can deal with it ok.

Would it be ok to have a few gallons in the fresh tank for use while in transit, but then flush the system as described above when re-hooking up to city water at the next camping location?

Any ideas / opinions about this would be appreciated.