That's the best description yet of that phenomenon Foul taste and it stayed with me all day too.I don’t know these billys, is there a lid?
If not, then it’ll probably be smoke. I had a foul cup of tea years ago boiling the billy on hexi blocks. Not only did it take about half an hour to boil, it tasted vaguely like chemically polluted fish.
Oh, that'll do it. Also, how long are you taking to boil? The longer its in that tarry smoke the more the grotty taste will stick, especially if you are hanging the pot quite high in the air. Using the lid, a hotter fire, get the pot closer to it ... all help in that particular area.pine wood with a high resin content on the fire.