How to CLEAN alcohol tank?

dear gals & guys we have an old alcohol tank ...that has black inky slime that will not pour out ... but you can hear it sloshing around...any ideas ...the rubber stopper finally came out....has air stem ... but supply line is clogged ... want to "bench test" oven before I install it.. but black slime and supply line (feed) needs to be cleaned .... any ideas? edward