For sometime now, when I wake up in the morning I have to cough up some rather ropey high viscosity crud. If any of you had that problem, did using a CPAP machine do you any good?

Do you snore, rather heavily?
If so perhaps a sleep study is needed.

I am pretty sure you have to have a sleep study before you get a cpap. They are known to push gunk from the sinus to the throat.. I use a netty pot or take a decongestant when I get stuffy. Otherwise it feels like I cannot breathe

Not sure stuffiness or snoring is the problem. Sinus drainage may be the reason, but I was wondering if the moisture from the CPAP might make it easier to clear the pipes. Back problems necessitate a good bit of sleeping in a recliner and the problem still occurs after a night of being semi reclined.

Before I had my CPAP, I would often sleep with my mouth open, leading to dried throat and/or mouth. I also had a lot of sinus troubles, as in always catching colds, sore throats, etc. The humidifier on the CPAP seems to really help me. Not only do I sleep with my mouth closed, but my sinuses are much happier. Before CPAP, I would catch cold 3-4 times per year. I have only had 2 colds in the 5 years since I started with the CPAP. Anecdotal only, but I'd say they really do help my sinuses.