Harvesting Poison from a familiar

Crafting and Harvesting Poison (p258 of the DMG) Says that a creature must be dead or incapacitated before you can make a DC 20 nature or Poison kit check to get a single dose of poison.

However, It seems to me that this system is for collecting the venom of random encountered creatures. If I have a snake familiar, could I not just command the familiar to bite a jar with a thin leather membrane to collect the venom? Would there still be a need to incapacitate the snake or make a check?