Yeast starter confusion

Can someone clear up some questions I have in regards to yeast starters and reusing yeast? As of now I have been just pitching White labs yeast from the vial or rehydrating my yeast a few hours prior to brewing up a batch. I have also started washing and saving the last few batches of used yeast and built a DIY stirplate with intentions of making big healthy yeast starters.
So I understand that if I buy new yeast and some DME and mix it up I will have a starter. My confusion is, if I decide to reuse some yeast slurry out of the fridge do I just pitch it or do I throw it on the stirplate for a night with some DME?

Thanks,

I would still make a starter to see if it is still good so that you don't ruin a $40 batch of beer.

Use mr malty. Com and calculate your starters for using smack packs, vials, or sachets of dry yeast. If you are repitching slurry it's a more or less
Kind of thing... You can pitch washed yeast straight after letting it warm up a bit so as not to shock it, or you can make a starter with it. In the later case I would adopt a "more is better" attitude and either pitch the whole amount of washed yeast from a single brew or make fresh... It's up to you but most don't re-use yeast past 5 brews to maintain the integrity of the strain your using.

Mrmalty.com has a lot of information on starters.

Use dme to make your starter wort, cool it to about 68°, then pitch the yeast into it.

Mrmalty also has a tab for using the slurry from a previous brew or from washed yeast.

It depends. I reuse yeast from 4 OZ jars that I peel out of split starters. In that case I would treat it like a commercial vial and use it to prepare a starter. On the other hand, if you are bottling and brewing the same day and pitching directly onto a yeast cake a starter is not needed. In fact, most sources I am aware of say that an entire yeast cake is overpitching and only half the cake is required. If you want to reuse a cake but are not brewing the same day, I would wash and store the yeast in a sanitized container in the frige to ensure it doesn't pick up any nasties while its waiting for the curtain to go up on the next act.

Thanks guys! Yes, I have been cleaning my used yeast and dividing it into two sanitized mason jars. I will look for Mr. Malty and learn some more as suggested. I will be brewing on Friday so I will pull out my stored Hef yeast and mix up some DME and use my new homemade stirplate. It sounds logical to see if the yeast starts fermenting and is viable prior to using the old yeast. I really think I will only use yeast once over then start again with some new store bought yeast. Thanks for the quick replies!