The following is based on a 0.4mm nozzle
[gcode_macro PURGE] description: purge filament gcode: ; ; simply purges enough filament to flush the tool ; G90 ; absolute positioning mode G28 ; home G1 Z10 F300 ; raise Z by 10 to be safe G1 X67.5 Y0 F6000 ; move to start of purge line G1 Z0 F300 ; drop nozzle to plate surface M109 S220 ; heat extruder and wait G92 E0 ; reset extruder G1 X67.5 Y0 Z0.4 F300 ; move to start xyz position G1 X167.5 E80 F400 ; draw the first line G0 Y2 F120 G1 X67.5 E60 F400 ; draw the second line G0 Y4 F120 G1 X167.5 E30 F400 ; draw a third line G1 Z10 F300 ; raise Z by 10 to be safe G92 E0 ; reset extruder