Originally Posted by bzwyatt
Some of the flavor will get from one to the other. I'd reuse the IPA, cause porter has a little hop flavor, but IPA doesn't have any chocolate/roast flavor. But it is probably not enough flavor to notice anyway. And yes, any yeast that has fermented a beer can do it again, whether it is dry or smack pack or vial.
I disagree with this. This is an old myth that has been proven wrong many times. If properly washed, then the yeast will transmit essentially no flavor. And properly washing yeast is really easy. And unless you simply drop the IPA on top of the porter yeast cake, you probably won't get any porter flavor carrying over anyway.
I use almost exclusively US-05 for my beer. I wash my yeast and keep track of how many generations it has been from the original packet. I don't know what beer the yeast has come from and I make a large variety of beer. I have never gotten a hint of porter or stout in any of my blondes or cream ales.
I say go for it. The order really doesn't matter if you use it properly. Learn how to wash yeast and reuse it. Build a stir plate, it's worth it and it really isn't that hard. US-05 is relatively inexpensive, but when you start using say, a Belgian or a lager yeast, and you have to buy two $7 vials, all of a sudden these skills and equipment will pay off VERY quickly when you can reuse yeast or build up your yeast count with just one vial. Or even harvesting yeast from a bottle conditioned commercial beer. Good luck.