No problem JR. Since the only time you want water going back to the main tank is while you are waiting for the heater to make it hot, once the water is hot you can chose to shut off the flow back into the tank via the solenoid valve. The water pump which supplies the heater is all you need . It pumps water through the heater, to (or past) the spigots and back into the tank (if the valve is open).
From the practical side I use a separate pump for hot and cold water because the Ecotemps are fussy about both pressure and flow rate. I generally leave the solenoid valve open the whole time I am using hot water as the 3 gpm pump Ecotemp recommends easily supplies the spigots and return line as well. I found this practice also helps stabilize the water temperature at the spigot because the heater isn't cycling on and off.
I have a 60 gal water tank and the returning hot water begins to show itself in the temp of the fresh water when Its down to about ten gallons. Since the Ecotemp heater is capable of heating incoming water 30-35 Degrees F above ambient, the heated stored water can set up a scenario where the heated water gets hotter and hotter to the point in my case where the PVC pipes swelled and a joint failed. I solved this problem by installing a programmable thermostatic switch to sense the temp of the water comming out of the heater and to shut off the burner when exiting water temps reached 109 degrees F. That solved the problem. I have several of these controllers in use and they work great--less than $10. Jack
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