4-quart yeast starter for 5-gallon lager?

I'm planning on brewing my first lager next month, and as I understand it, I'll need to use a liquid yeast with a yeast starter. But crunching the numbers, it looks like I'll need to pitch around 400 billion yeast cells (4 billion * point of O.G. per 5 gallon batch, then doubled because it's a lager). A 2-quart starter will give me around 200 billion cells, so this is where I run into my problem. It looks like I need 1-gallon starter.

How do you do a 1-gallon starter? I have a 2-liter Erlenmeyer flask, and I'll be building a stir plate in the next couple of weeks, but that's only half as big a starter as I supposedly need. Do I do a 3-stage starter (1 quart, then 2, then 4)? And when I get to the 4-quart starter, what type of vessel should I use to contain so much frothing liquid? Over how many days should I be doing this?

And finally (and possibly most importantly), do I just dump the entire gallon of liquid and slurry into my fermenter? Won't adding an entire gallon of plain-DME starter wort into 5 gallons of precious beer wort dillute the flavor? And if I use a 6.5 gallon carboy, that only leaves me 0.5 gallons of headspace - isn't that just asking for a blowout?

Looking for some voices of experience here! Thanks!

What you need is a couple of 2-liter flasks. You make 1 2-liter starter. Once that is done cold crash it so all the yeast is caked on the bottom. Decant as much of the liquid as possible. At this point the second flask should be ready with 2-liters of starter. Dump the yeast from the first flask to the second. Once that flask is done fermenting out, cold crash again. Decant the spent liquid and dump into your wort. This entire process could take up to a week to complete.

Thanks arnold. So I don't actually need all that liquid - just the yeast cake? I currently only have a single 2L flask. What if after cold-crashing and decanting off the first round, instead of transferring the yeast to a second flask containing more starter wort, I instead just replaced the decanted liquid with fresh starter wort on top of the same yeast cake in the same 2L flask? I could prep the second batch of starter wort in a plain old pot on the stove, then chill it and just dump it in - would that accomplish the same thing, or is there a reason you're recommending transferring the yeast to a second flask?

Nope... that would work. After it finishes fermenting just decant the liquid off and pitch the yeast.

Yeastcalc.com

Do a stepped starter. Do the first step, cold crash overnight, decant, add the second step of wort, let it finish, cold crash, decant, pitch. That way you only need one flask, a sauce pan to boil the second step, and maybe a funnel to help pour it in to the flask on top of the yeast that you accumulated during the first step.

Just be sure to cover the liquid in the sauce pan with some foil. Don't need any bad things getting into the starter that you worked hard on.

i use a 1 gallon carlo rossi jug. works perfect even with my stir plate.