Reusing Yeast

I would like to use the yeast currently in the fermenter (Wyeast 3726) to do our next 3 batches. We will be doing another saison, an IPA, and a porter. (I know it's not standard for this yeast, but we're going to give it a shot).

Can we use the one cake for all three batches, or should we wash it, pitch into a starter and go from there? I know people pitch directly on the cake, which I'm comfortable with, but I don't think you can do that 3 times in a row.

What would be the best approach to reusing this yeast 3 more times?

I would say wash the yeast first. There is a yeast washing sticky if you haven't already read it, it will help you with everything you need to know to wash the yeast.

Pitching onto a yeast cake can actually cause some problems associated with over pitching, so it is usually best to harvest the yeast, wash it, make a starter, and then pitch. Washed yeast should last a few months if it is done properly.

I completely agree. Wash that yeast, and split it into three containers. Pitch each when your batch is brewed -- they should store for many weeks once washed.

If you pitch them sequentially on the previous yeast cake, you are going to (1) have residual flavours left over from the previous batch, such as the hops from the IPA which may not be welcome in a porter, and (2) the yeast count will rise and the health will diminish with each re-use, inevitably leading to fermentation problems and potential off-flavours.

to avoid the over pitching problems you could always just dump out part of the yeast cake the 2nd time you pitch.

Can I scoop out what I don't need for the next saision and save that for the other batches?

It seems like it would work. We have been straining our wort before it goes into the fermentor, so the cake should be fairly clean.