BIAB...2 pot boil.

I'm sure this has been done, but I can't find anything through the search.

Here's my set up: I have a 5 gallon pot so I usually do a partial boil, and top off at the end. I always partial mash (in a bag) in my 5 gallon pot as well.

I'm thinking I could easily mash 8-10lbs of grain in my pot for a low gravity recipe. The question is, do I sparge until I hit 4.5 gallons or so and then top off at the end of the boil, OR do I collect as much as I can in my main brew kettle, and then collect another 2-3 gallons in a smaller kettle.

(I would actually collect all of the wort in my fermenter first to make sure both pots were the same gravity, and to check my efficiency. Then split the wort between my 2 pots.)

I would continue my boil in the larger pot as usual...hop additions and all, but in the smaller one I would just boil for the 30-60 mins to get rid of DMS. I would then chill both and combine in my fermenter.

Does anyone have any experience, or see a problem with this method? Any and all input is needed, and appreciated.

-Thanks

EDIT - I was thinking of doing a Mild for my first all-grain experience. Low gravity, simple, quick turnaround.
https://www.homebrewtalk.com/f67/reapers-mild-1st-place-2011-hbt-competition-239228/

The ways this can be done are almost too many to count...that being said, I would treat it as two small independant BIAB batches using both pots, each with a bag splitting the 5 gal batch b/w both kettles. Not a great idea to use your fermenter for unboiled wort FWIW as there are lots of lacto bugs in the unboiled wort.

I agree with Wilser there are so many ways you can do it, and also on not using your fermenter for wort collection. To be safe, I would use another pot if you can.

Here is one thread that talked about split boils: https://www.homebrewtalk.com/f36/advice-first-biab-all-grain-316982/

I have been doing 2 pot BIAB for dunking in sparge water, but I only run off what I can boil in my biggest pot, so haven't tried splitting larger boils. The trick is finding an easy way to combine your 1st and 2nd runnings pre-boil, then split them again. With the increased volume, it also makes the wort transfer harder. It almost takes the inherent simplicity out of doing BIAB in the first place. This has been the same thing I've fought in my setup.