I BIAB and I do use a 7.5gal pot to mash in. I sparge in another pot (or previously, I put my first runnings in another pot and sparged back in the BK) then combine the first runnings and the sparge and boil. For a normalish gravity beer, my preboil is usually around 6.75 gallons, so it's tight, but with fermcap and close attention, I can avoid boilovers.
I highly recommend the turkey fryer BIAB method for no-frills dirt cheap all-grain brewing. I don't think I'll upgrade for a very long time.
I can't be arsed to keep up this list of what's in the fermenters, but hey, check out the cool brewery I own!
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