Liquid tight welding, please help

[joefreel]

hello i have a welding project for a friend tomorrow and i am building a steel box designed to hold liquid the box will be 2x2x3 or so, so it is small but i must not have leaks so my question is would it be better to weld the inside or the outside, or both? i also may have to put a drain valve in the bottom and also a lid on the top so will i need some sort of vent for the top?

[snoeproe]

Any pressure going to be in the box?
Outside is more easy to weld and get at. Welded outside will be more visibly attractive to the eye as well.
Drain valve is not hard. Drill or cut your hole, weld a pipe coupling on the bottom side of the hole. Add a nipple then the valve. Use a pipe plug in the the other side of the valve.
What welding method will you be using? You will have to fill the tank with water to test for leaks when your done.

[dondlhmn]

You don't stay what process you are going to use to do the welding or exactly what kind of joints you plan on making, but whatever you DO use, be sure to not leave any craters anywhere! I learned this the hard way and had to redo a couple of welds that leaked in a couple of spots where I left TINY craters when I applied pressure to check tank I made. Granted, the thing didn't leak until I got about 50 PSI in it, but then it did show some tiny bubbles (Hey, wouldn't that make a neat song title?) when I applied the soapy water solution to it on all the welds. Even if there is not going to be anything above atmospheric pressure in what you are making, fluid (especially with gravity's help!) will find a way out and there may be, at the least, seeps where ever you didn't get a good fill.