Possible to do 3Gal BIAB in a 4Gal pot?

I usually do one all-grain batches but am planning my first 3 gallon; it will be brew in a bag.

Is it possible to do this in a 4 Gal pot? The reason I ask is because I live in the middle of nowhere and the only place selling stainless steel stockpots has a 4 gallon for $29 and a 7.5 gallon for $89. If I can avoid having to pay the extra $69, it's a bonus.

If I can use the four gallon, how do I top things up at the end, as I'd imagine I'd lose a lot during the mash and boil. Is it possible to just litrally top the kettle up with water at the end, to reach 3 gallons? Or add it to the carboy?

You can top off near the end of the boil but it is not recommended. Plus your going to loose a ton of water. I bet it would be close to half if you have a nice rapid boil along with the water you lost from the grain. Imo and in my experience I would buy the bigger pot. It will save you the hard ache and you can do bigger batches later down the line. Or big bears. A big beer would be to hard in that little 4 gallon pot. Also try looking into an aluminum pot if you don't wanna spend and arm and a leg. You can get a huge pot for a great price. Just gotta build up an aluminum oxide layer which is very simple to do

I can only run 2.5 gallon batches with my 4 gallon pot and that is using a cooler mash tun.

Doe anyone in your area sell tamale pots? My first brew kettle was a 32 qt (8 gal) aluminum 'tamale and safood steamer,' that I paid about $20.00 for at Walmart. I used it for several 5 gal batches, before I was able to upgrade to a stainless steel pot

This picture from Walmart's website looks like the same pot, except that mine came with a glass lid. Warning: if you stick that insert in, you may never get it out again - at least without mangling it and scratching up the pot. Ask me how I know...

Ya I paid 50 dollars for a 16 gallon tamale pot. Works great! Would order one online. It will save you money, you will be able to boil big batches, and it boils faster since it conducts heat better.

You should be able to do 2-2.5 gal of wort and top up to 3 gal at the end if you want to use that pot - you might have to do a sparge. I sometimes make a 5 gal batch on my 3 gal BIAB set up, i.e. make a concentrated 3 gal wort then top up to 5. I can only get up in the 1.050's that way, but I see no difference in quality between those batches and the same recipe full volume boil. Revvy has a whole write up on it somewhere.

Edit: to answer your question about topping up, just add it to the fermenter. I use my tap water treated with campden but you could also just top up with a gallon of spring water.

I'd also recommend springing for the larger pot to start with. You can brew small in a big pot, but not the other way around. If / when you go to 5 gallon batches, that bigger one will be (barely) big enough to work with.

I live in the middle of nowhere too. Amazon is your friend. With free 2 day prime shipping I can usually have it quicker with no gasoline cost than venturing out to the nearest big town (relatively speaking) searching for the limited choices offered there.