When you set up your crock pot, fill and set your jug slightly higher than crock pot, fill jug with water, hose going from the bottom of jug, (you don't want hose to suck air when water level gets to the low mark) to crock pot, blow in to jug with mouth over opening of jug, and it will siphon into crock,when it gets to a full level in crock pot , mark jug where water level is and that will roughly give you a starting point on where your full mark is on the jug and should be roughly the full level in crock pot.
Make your low water level mark high enough on jug, so there is still a good amount of water left in jug in case you can't tend to it right away, and keeps it from sucking air.
You can fine tune it after that.