There seems to be some confusing regarding the actions that Elittose has taken and why. From posts #1 and #5 it seems that:
1. The initial problem was that city water was causing the freshwater tank to overflow.
2. Elittose replaced the water pump to fix that problem.
3. A new problem started, the new water pump was pumping water out of the city water connection.
4. Attempting to fix the new problem above, Elittose replaced the water pump again (which really had nothing to do with the new problem).
5. Because the second new water pump is also pumping water out the city water connection, they are now here asking for our advice.
The solution is that the check valve in the city water connection itself, not the water pump, needs to reseat - or the city water connection itself needs to be replaced. As an alternative, a 3/4" GHT (Garden Hose Thread) plug or shutoff valve could be screwed into the city water connection:
https://www.homedepot.com/p/Orbit-3-...7933/100659291
or
https://www.amazon.com/Camco-22103-R...dp/B00Y52IOHA/