The gas tank is out and sitting on the ground. I need to solder a fitting back on without blowing myself up. I've done this before by washing the tank out and letting it sit in the shed for a few days first. But I really would like to turn this repair around today. Any ideas how I can safely get a flame close to an empty gas tank? I've thought about just filling it with water, but I fear the water would absorb the heat and make soldering impossible. If I wash the tank out, how can I get the residual water out before reinstalling? Would swirling a few bottles of 90% rubbing alcohol around in it do the trick? Can anybody think of something better to use, something that is fairly readily available off the shelf?

Get a small gas engine eg lawn mower, edger, etc. connect the muffler to a small flex pipe. Flex conduit is fine. Secure it into the opening of the tank. Start motor. Weld. The CO from the motor pushes the o2 out so no explosion. Seen it done many times at the welding shop near where I grew up.

A friend of mine that did welding said the best way to deal with a gas tank is to wash it thoroughly 3 times, steam the inside twice, and then give it to someone else to deal with. :)

For drying out a (car) tank, I used a shop vac to blow air into the tank. It naturally heats the air a little and after 45 minutes, it was bone dry.

We soldered with the tank full of water. A small bubble of space at the top won't let the water absorb all the heat or allow enough gasses to collect to be dangerous. The only thing special I recall doing was adding a few bottles of gas line antifreeze to absorb any residual water.

What can I use to get water out of a gas tank | Good Sam Community

opnspaces
Navigator II
Mar 08, 2020
Thanks everyone. I finally braved it and filled the tank with CO2 from my tire inflation tank. The tank is soldered and back in service.
Dusty_R
Explorer
Mar 08, 2020
Big Katuna wrote:
Get a small gas engine eg lawn mower, edger, etc. connect the muffler to a small flex pipe. Flex conduit is fine. Secure it into the opening of the tank. Start motor. Weld.

The CO from the motor pushes the o2 out so no explosion. Seen it done many times at the welding shop near where I grew up.

X-2
time2roll
Nomad
Mar 08, 2020
For a small amount of moisture... just fill the tank with some of that special gasoline blended with 10% alcohol.
Big_Katuna
Explorer II
Mar 07, 2020
Thanks for sparing us. :-)
wa8yxm
Explorer III
Mar 07, 2020
As for getting water out of a gas tank after it's had water in it. Of course most of the water you can remove by traditional methods (pour or siphon or pump out The rest that remains is not as big a problem as it used to be in days of old when folks were bold and used 100% gasoline in the tank.

YOu see small amounts of water can be absorbed by small amounts of alcohol and then pumped into the engine and turned into steam.

E-10 anyone.. (usually they used around 2% back in the days when the ad was "My Advice Sir, Get De-Icer" (HEAT brand gas line antifreeze. Pure alcohol)

I remember those days and have a few "War stories" about them in fact. but not today.
naturist
Nomad
Mar 07, 2020
91% isopropanol, cheap at the local pharmacy, is soluble in both water and gasoline. So buy two quarts. Drain the gasoline as best you can, throw in the first quart of alcohol and swish around throughly, dump out, then fill with water. After solder/weld, drain, throw in the second quart of alcohol, swish, drain, and fill with gas.

Many years ago, I had to patch a hole in a gas tank with an arc welder. Didn't bother with the first quart/swish but did fill with water, which worked fine and was most helpful in not simply blowing holes in the thin sheet metal with the arc. Alcohol rinse and filled with gas, no problems.
Johnny_G1
Explorer
Mar 07, 2020
Big Katuna has it right, welded up many tanks that still had gas in them. would just run the vehicle and put an exhaust hose in the tank.
opnspaces
Navigator II
Mar 07, 2020
^ Of course, this is one of those "if it was a snake it would have bitten you" moments. I have my CO2 tank for inflating tires off road. I can jam the hose into the tank with a rag and wait for it to fill with Co2. It does make me nervous though even knowing that Co2 is heavier than air and will fill the tank up. Science may tell me it's okay, but my self preservation mechanism is still screaming this is a bad idea. And I usually listen to that voice when it's this loud.
TenOC
Nomad
Mar 07, 2020
Get some dry ice at the grocery store crack in small pices and put in the tank. Dry ice is frozen CO2 so allow a few minentes for the ice to melt and fill the tank with CO2.
2oldman
Explorer II
Mar 07, 2020
Perhaps you already did this:

Google: water out of gas tank.