Yeast Starter from Production Beer?

I've read about the Wyeast starters and how to make them, but I have seen mention of getting yeast through partially drank craft brews. I am making a DIPA this weekend and wondered if I could get any tips on how to replinish the yeast from a craft brew IPA or if it is even possible?

It's posable but probably not by this weekend. First you have to find a non-filtered non-pasteurized beer (not that hard). Then pour most of the beer into a glass and drink it. Sanitize the mouth of the bottle and a jar. Swirl the beer around and pour it into the jar. Next make a very small starter, maybe a cup or so, and feed it to the collected yeast. Once the starter has run its course, chill it, pour off the spent liquid, and repeat with a larger starter. Keep this up till you have the amount of yeast you need.

Well, thats interesting if not incredibly cool to know I can do that. I have the dry yeast I can rehydrate and pitch. I think i'll do that.

Here's a whole thread on the subject and list of beers you can harvest yeast from.

https://www.homebrewtalk.com/f163/commercial-beer-yeast-harvest-list-262713/