I use a cooler aslo. This is how I do it. After an hour of letting the grain mash (all grain brewing). I then add 1-1/1/2 gals of boiling water. then let it set for 5-10 minutes. I then start a slow dain. On the side I have a pot of boiled water. I then add 2 quarts at a time, just to keep the grain bed covered. I continue this method until I reach my pre-boil mark. I aslo have a low flame on my brewing pot while it's filling. Heres a pic
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