I am exprienced DIY, but I have new project to install a tankless water heater. The mfg requires the pressure in the gas line to be with 4. to 10.5 w.c. (aprox 1/8 to 1/2 PSI). What is the procedure for testing the gas w.c.? I know I need to disconnect the tankless water heater to do this. By the way, I did test the line for leaks.