Reusing yeast, and beating a dead horse

I know I've already asked about 10 questions in regards to reusing yeast.... but I've got a few more

I have a carboy that's been sitting in the garage for the last 3 weeks, with a large yeast cake in the bottom and an inch of beer on top of it. There is an airlock on top.

Am I still able to wash the yeast and use it? Can I pitch right on top of it?

I guess my ultimate question here is, I need a large starter for my next brew. Should I just go buy some new yeast and make a starter?

If there is a single living cell, you always _can_ use the yeast. I build all of my starters from exactly ten frozen cells and it works fine and dandy

In the question of whether it is a good idea depends on two things.

1) Sanitation. When dealing with small quantities of yeast, sanitation becomes insanely important. You want to be careful at all times, of course, but 100B healthy cells is going to fare reasonably well enough against small infections. When dealing with small quantities of dormant yeast, though, it's much harder. Sitting under an inch of beer, your yeast is still clean, but you'll need to be careful in how you harvest and wash it.

2) Number and viability. It's hard to know exactly how much yeast you've got under there. Mr Malty's pitching calculator is as good an estimate as you are going to get without a microscope. If you want to harvest and pitch that yeast, use the numbers suggested to you on the Mr. Malty calculator.

Either will work well enough. It's just a question of time vs. money.

I too have the same situation. I racked my Maibock from a carboy, leaving just enough beer to cover the yeast cake. I had intended to wash the yeast but I got the flu.

I was considering dumping it, but I really would like to wash reuse that PacMan yeast.