What sort of taste is it? If its a taste approximately of "ass" or like peanut butter, that would be epsom salts. If you used them to dry your acetone you didn't dry it enough and/or filter it properly.
If there is free water in yer acetone and you've put dehydrated epsoms in there - but not enough to remove the water - they will have become hydrated, then dissolved in remaining free water and still miscible with the acetone. Make sure when ya nuke or bake the salts, that you use the hard "chunks" and not the fine powder.
This would help explain what you see as the substantial losses to rinsing. Always keep your rinse acetone either way.