Water pump kicks in every 30 seconds

We have just sanitized the fresh water tank for the first time. After running the taps to clear out the anti-freeze, and topping up the tank completely, the water pump kicks in every 30 seconds with a half second burst.  To me, this would indicate that the pressure is dropping.  Is this normal?

If none of the valves inside are dripping, including the toilet, double-check the two low-point drains outside.  Then check the overpressure valve and anode opening on the water heater.  Then check the valve right behind your water pump, which allows you to switch over to a short uptake hose to suck in antifreeze, make sure that isn't leaking.

Yes, you can get a socket wrench on it, I forget the size.

Thanks a lot, guys and dolls.  As Bette said it was the anode.  Should have done the work before the sun went down.  Not having a 1 1/16th socket I improvised with an adjustable wrench to which I clamped  my vice grips as the lever.  This was an adaptation of a trick that my uncle showed me to loosed the tank bowls on a toilet.  You push really  hard on the screw driver and and use the vise grips to apply the torque.  By the way, don't let the screwdriver slip.  We finished flushing all the tanks and raised the stabilizers. Tomorrow we fill the fridge and head west.