1For liquids you are going to want to wait until your food is almost finished being grilled. Simply pour the liquid into the valleys at the last minute and let the steam bath of flavor begin! Use some prudence with liquor- don't forget that it is quite flammable.
2For spices, herbs and wood pellets you can sprinkle them into the valleys at the beginning of the cook, mid cook or right at the end. It all depends on what flavor profile you are going for.
3***Remember, whatever you put down in the valleys is going to leave some debris/residue***