Re-using yeast

I managed to save about 700 ml of yeast for a beer I plan to make this weekend.  It is in the flask now sitting comfortably in about 70F degree weather in my kitchen.  My question is, do I need to cook up some DME and add it to the yeast or can I just pitch what I've saved?

I looked at mr malty's yeast calculator but I'm not sure I'm using it right or if I understand it.  According to my calculations I'll need something in the neighborhood of just over 4 liters (according to his calculator actually, and my use of it).  Isn't that close to a gallon of yeast?  I don't think I've ever pitched more than a half liter ever and my beers have been turning out fine. 

700ml of slurry? How long has it been since you washed the yeast?  If it's only been a couple of days, you'll probably be ok to pitch it as-is.  Any longer than that, I'd mix up a starter wort.

I keep my harvested, washed yeast in 1/2 pint mason jars in the fridge.  A day or so before brewing, I mix up a starter using a ratio of 100g DME per liter of water.  For a 5 gallon batch or homebrew, 1-1.5 liters or starter works fine for me.  Boil 15 minutes, cool, and transfer to a growler.  I then decant most of the water off my washed yeast, shake up the remaining slurry, and pitch into the growler.  Air-lock it, and usually have good activity 12-24 hours later, ready to pitch into my wort.

Did that help?

I think the MrMalty calculator means total volume of liquid, so a 2L starter is 2L of liquid.  The drop-down box where you indicate your starter method then applies the growth multiplier, ranging from static starter on the counter (least) to a stir plate (max). 

The yeast requirements are driven by ale/lager, gravity and volume, so yea, a 10-gallon dopplebock of 1.090 may require 6L.  I was surprised on this 11-gal barleywine that it indicated 3.81L starter AND still using four Wyeast packages in order to get there.  We ended up making a 2nd 3L starter using yeast from the 1st one.