Following completion of z-pack for upper respiratory infection, how long might i expect it to take for lung fluid (mucus, white/clear) to clear up?

Same as w/o Zpak: While I can't speak for your current illness, most upper respiratory infections (URIs) are caused by viruses which don't respond to antibiotics such as Zpaks. As such, you can expect to get well in the same time whether or not you take antibiotics. We typically recommend avoiding antibiotics for URIs b/c that just sets you up for antibiotic resistance (won't work in future).