How do I open cement sealed threading?

I want to remove the valve assembly off of the font, how do I remove it. Is blow torch enough or boilling water and acetone/automatic transmission fluid mix?
Will it melt the bung or whatever is holding the bung in place? Can someone pls help me or tell me how to use heat to make it open, I also can't afford destroying the bung.

It's a cement sealed (gasolia I think not sure, I think it's also lead based) valve assembly on a coleman 249 scout which was made in 1958 in Australia under licence from Coleman canada.

Helppp

 

Hello @Desolate_Place ,can you attach a picture of what you need help with.
If you want to remove the fuel pickup and shutoff valve. Do not heat it up.
Do you have a vice? If so tip your tank upside down. Careful close the vice. Not tight. Then you can use the tank as leverage and you won’t damage the pickup and valve.
I hope this helps and thanks for your post, plenty of good advice just ask

 

Hey yes your correct, I'm trying to remove the fuel pickup thing, I want to completely remove the valve assembly from the base of the fuel tank. I don't have a vice, is there any other way?
How hard is it to get off? I'll look at vices on eBay, is there any other way that won't snap the collar.
It won't let me upload photo because they're wrong file format. Google Image Result for https://i.ebayimg.com/images/g/44QAAOSw0wRjyvzV/s-l1200.jpg
Here is image of the valve assembly in talking about.