The valve is brass, has 1/8" mnpt into the tank and a compression fitting,1/4" on the outlet. It works like the drain on the radiator or an engine block

1941 Chevy
"First rebuild - complete!"
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1941 GMC resting peacefully
1946/1947 Chevy Street rod on s10 frame complete
1945 GMC panel truck in line for restoration
1941 Plymouth stock complete
1941 GMC COE in restoration process
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1941 Chevy Coe uncertain future resting now