How to re-pitch with for a tripel

I am starting my second Tripel and I see everywhere (including the recipe I have) that I should re-pitch yeast 3 days before bottling. How exactly do I go about doing that? Should I save some from my starter? Use yeast that was washed from the primary? How much yeast should I use? Will new yeast really stay in suspension for 3 days, or will it just settle out? Why can't I just shake up the yeast from the bottom? With no new sugar added won't the yeast just fall out?

Okay enough already. I know I have a lot of questions, and even the slightest amount of advice will be appreciated.
Also, sorry if this has been posted already, but after a bit of searching I have not come across an answer to my questions. Maybe I am just bad at searching.

There's no single best answer to this. The advice is given because a high-gravity ferment like a Tripel can leave the yeast so depleted it won't wake up. I don't know about the 3 days - I think it's fine to add it any time, including in the bottling bucket, as long as it's re-hydrated. It also doesn't take much (sorry, not very quantitative). Thus, you can use yeast from your starter or (my favorite) a neutral dry yeast, like Safale 04 or 05. The washed yeast from the primary would not be the best (because it's been through a high-gravity ferment).

I'm drinking a Tripel I had in secondary for 3 months... Didn't re-pitch, and it's carbed up fine...

That's not unusual. With good yeast treatment, it should be up to the task of carbonating. What vespabrew is asking about is insurance. If you've ever had a barleywine or Tripel that didn't carbonate, you'll realize that a Safale packet is really cheap insurance.

I like the idea of the safale. Thanks. The Wyeast gets expensive so I like the fix.