What size chimney/stack for outside fireplace?

[SickSilverado]

I was given an old diesel tank (hasn't been used for years), probably 100 gallons or more. I cut a door off an oil field water gate and had it welded on. I guess I'm trying to make a fireplace since I don't plan on cooking with it. I made a small fire in it, but the smoke mostly came out the front. I'd guess the exhaust opening was too small or too far back from the fire(4.5" pipe in rear corner)? I have some pipe here to use as a stack but not sure about placement. I have a 10" and posibbly a 6" pipe to use. Should that stack be directly over the fire? I'd like to use the 10" pipe and perhaps put a damper/cover to close it off some if needed. Any advice?

 

[csp]

The lack of height on the pipe in the rear corner didn't help. You need that height, whatever size is appropriate, to draw the smoke up and out.

 

[SickSilverado]

I want to use the 10" pipe at 4ft tall (making the whole unit 8ft). But that's just based on appearance. I plan to block off the 4.5 pipe. I just want the smoke up and out of our faces when we sit/stand around the fireplace. My dimensions are 46" tall, 36" wide, 20" deep, and a 20" diameter round opening.