vertical line starting from pump top vertical nozzle: weight for spring?

i have to install a spring on a vertical pipe starting from top nozzle of pump to decrease load on pump top nozzle.
the pipe run vertically for about 3 meters and then goes horizontally.

For a (variable) spring hanger: have i to consider the vertical pipe full of fluid (a liquid having double weight of water) or have i to consider it empty?
Vertical fluid column (inside the vertical pipe) insist on bottom of pump and not on flange connection between pipe flange and pump flange nozzle (where i have to check flange load) : so, the spring hanger, i think, should not "feel" the weight of this fluid column inside vertical pipe.

Have i to set the fluid density =0 inside the vertical pipe (to avoid spring to support fluid weight that really will insist on pump bottom instead of spring)? or will this affect other caesar results? eventually can i set density (=2) and set a force on spring node equal and opposite to fluid weight so to discharge the fluid weight from spring?
what is the best way to have a correct spring load in this case? the pipe diameter is big (12") and fluid weight is high so i risk to order a wrong loaded spring hanger....

thank you