I have a vial of wlp400 that has a use by dec 12 2013 date on it. I was looking at kits to brew that use this yeast but wondering if it is still good or not.
Make a starter. Step it up a few times (500ml / 1L / 2L). Then brew something small 1.050 or less. Split the yeast cake into 2 mason jars. Brew two bigger beers. Rinse, repeat 
I have been making starters but the rest of this ^^^ has me lost. I’ve yet to reuse yeast so I’m not familiar with the rinsing process. I would definitely like to start as that would save some cash on brew day.
Just make a small starter with it, I’d go with 1 liter. If nothing happens, toss it. If it ferments the starter, let it finish and settle to the bottom, then decant the clear liquid from the top and pitch the yeast on the bottom into a bigger starter, whatever size you need for the brew you will be doing.
Repitching yeast is a whole nuther subject that can be simple or complicated depending on what you are after. dobe12 is suggesting a moderately complicated method that involves washing the yeast between reuses. I’ve tried that, and found no compelling advantage over simply dumping in slurry - complete with trub - from the bottom of the fermentor.
+1
Rinsing yeast is fine if you have the time and inclination to do it, but it really is an optional and largely unnecessary step.
If your sanitation gets the proper attention every step along the way (not to mention while transferring the slurry to save it), repitching (usually just a portion of it) as is will be perfectly fine with no detriment at all to the beer…even when repitching through a few subsequent generations.
It was actually just a joke (wash, rinse, repeat…). What I meant was step up a starter. Start small, 500ml, then got to 1L, then 2L. That should give you enough yeast to brew an average beer (1.050’ish). Collect the yeast from this batch and use it to brew 2-3 more beers and so on and so on.
I use to rinse yeast, but have gone to just collecting the slurry as well. It’s worked out just fine for me and there is WAY less chance of messing up the yeast. I agree with you guys. My early comment was simply a joke.
