We just added roaster or slow cooker and slowly raised the temp. When it starts bubbling, that is the moisture coming out. When it stops bubbling(all the water is gone) we scoop out the chunks and then poor the fat into jars through a strainer. You could try and scoop the fat out by layers into jars so that it is sort of stratified. Probably separating the different fat types before going in cooker would be helpful. Seems like you know all this if you made it before though. I'd be nervous about adding water if it's to hot and steam explosion. I would also think adding water would allow it to go rancid faster.