New member with questions

I am new to this forum and am excited to connect with others who are in similar situations. I am 67 years old and was diagnosed with MAI/Bronchiectasis in 2013. At that time my ID and Pulmonary docs suggested a "watchful waiting" course of action as my sputum cultures were not consistently positive and my CT scans did not show advanced disease. However the disease did progress and I started therapy with 3 antibiotics 9/2018 (Azithromycin, Ethambutol and Clofazimine. ( I had a febrile reaction to Rifampin hence the Clofazimine as a 3rd drug replacement.)
I take all the usual precautions to prevent micro aspiration and I now have an an odd question: My dentist recommended I start using a Waterpik water flosser (for reasons completely unrelated to the MAI diagnosis) and I am wondering if any of you have heard of any concerns about micro-aspirating of water with use of a waterflosser?
Another question I have is: I tend to not produce sufficient sputum for a specimen until evening and by then my lab is closed. I'm wondering if it's possible to keep a collected sputum specimen overnight and take it in the next day? And if so should it be refrigerated? I have asked this question of my MD and he wasn't sure and just said that I should take it in the same day but he didn't have any specific information to support that.
Thanks in advance for any helpful responses!