I don't know about oxymetazoline but steer clear of xylometazoline, that kind of decongestant is far too easy to get dependent on (meaning you will start sniffling again once you stop taking it).
Yes it is likely your K is cut, I have experience with cut powder and pure crystal and the powder usually tended to clog up and fuck up my nose. Find some vials to cook yourself and/or give your nose a break. I've been in the same situation as you describe and there weren't really other options that I know of. (Well I won't advise you to start IMing lol, and you need pure product for that as well anyway).
Snorting saline is also a good one yes, just stick your nose in a glass of water with a spoon of salt and hack that mother up, then spit it out.
That should be done frequently and it is likely to cost you more product that is lingering and flushed, then again - the question begs if that K would have been absorbed otherwise.