Cleaning stock fuel tank

[EvoLuTioN]

I'm currently cleaning my fuel tank and I'm been cleaning it with hot water and soap, but I also want to get this "foam" that some people has been telling me about, I know firefighters and the military uses it for fire, where can I get this commercially? It basically covers the gasoline and prevents it from mixing with air, aka no ignition when welding my sump onto it

 

[Typhoon]

Only safe way to weld a fuel tank is to get the insides DRY, and fill it with an inert gas.
Do not take a shortcut here.

Regards, Andrew.

 

[Kckazdude]

The best I can suggest is to flush it out really well with air and water. The more you can air it out the better. When I would repair motorcycle tanks I would fill them water. I can only remember one flashing on me that way. I didnt have it even half full of water. Was in a hurry to get it finished.

 

[cjsupra90]

I have always filled tanks as much as possible with water and then purged the rest of the volume not filled by water with argon. I have never had a tank flash or explode on me.