I suspect that what's happening is that when you open the 2nd faucet there is enough demand for the water pumps to kick and you are getting full flow. The regulators are actually terrible at getting much of a flow rate and highly restrict your water flow. I keep my tanks full and use the pumps only as they provide the best water pressure. You can also get a better water pressure regulator that has better water pass through. There are several but they are a bit more expensive. These will have a dial where you can select the pressure output you prefer (and it does not have to be 45#) and get the flow you like.