take can of paint. spray upside down, relive pressure/gas.
take can opener, while holding can upside down use opener to cut off bottom.
if it explodes. consult a physician.
if it doesn't explode like shrapnel in your hands, pour it into marker or container.
if you're using a foam tip the xylene in the paint will melt it. your best off using a metal tip marker. if you have one already just pour straight rusto from the pint in there.