To devour, grab a host with Ctrl + Click or Grab intent (3 in hotkey mode) then click yourself, standstill. To stop the host from getting up and running away, you can switch to an empty hand (X in hotkey mode) and keep tackling them using Disarm intent (2 in hotkey mode) when you are devouring them. Xenos with devoured humans inside them can not vent crawl. (Edit this template)
Usage
Add {{Devour}} to all xenos, so you don't need to change them one by one if this changes.