The SP-580Q Imprex II Hyperdry snorkel has a special internal purge channel located below the mouthpiece. It channels exhaled air out the top of the snorkel while excess water drains through the bottom purge valve.
Have logged over 1000 sport dives in the last 46 years. Used lotsa snorkles over the years - - some good, some bad.
This one works about the best of any I have used.