reusing yeast on back-to-back batches.

I'll try to keep this simple. I have an IPA fermenting right now (1.062) and a friend will be brewing an IIPA (1.087) soon. He would like to use the yeast from my current brew when its done in the primary. The yeast is WLP002. From what I have read it's not wise to pitch directly on the cake as that would be over pitching. What is the best way to do this?

How much of a time gap will you have? If a week, or so, then you could just wash the yeast from your brew and give him a jar of it to pitch into his... Use Mr. Malty to figure out how much of the slurry he'll need and go for it... This would also let you keep some of the yeast for your own batches...

I would advise using a starter if you go longer than about a month from when the yeast was washed/harvested to when you'll be using it. That way, you KNOW if the yeast is still good or not.

I dump right onto the yeast cake all the time. I take a sanitized spoon and scoop out about half of the cake and dump my wort right in. Takes off like a rocket.

You save a little on yeast and the time it takes to clean a couple of fermenters.

Removing half is probably about right for pitching a big beer. That's definitely the easiest method.

If you want to save more yeast than that, you should read up on the "Yeast Washing" sticky

I'd do it. Steal some and wash it for future batches if you feel like it. Else just throw half away and toss that wort right in!