Cardinal RV Club

Does anyone know if the pin weight becomes a little lighter if the FW Tank is located to the rear of the axles and filled?

Yep. It will increase the total weight and decrease the pin weight. Theoretically, you could put enough weight behind the axles to lift the rear of your truck. Although the weight of the filled water tank won't make enough difference to tell without a scale.

gmarker is correct, and its clearly visible with an air-ride pinbox. I have not weighed the difference, but my pin box needs a 5 psi change from empty to full on FW.