Looking after someone in failing health is fraught with tough conversations. But as challenging as unfamiliar and emotionally charged topics can be -- especially those that tend to flip our usual family dynamics -- they don't have to be forbiddingly uncomfortable. Talking is almost always better than ignoring, provided you prep yourself first on what to say and how to say it.
Talking about incontinence successfully starts with careful thinking. Know your role. If you're going to help someone, you need to be perceived as being helpful. Be the person's advocate, not an adversary. Anytime you feel strongly that a behavior is unsanitary, unsafe, or otherwise problematic, it's wise to get a third party involved. This sidesteps nagging and arguments and instead gives you the role of supporter, helping the person follow someone else's advice.
This distinction is especially useful with a touchy issue like incontinence. It's hard to stick to a calm discussion where you're kind and supportive when you're thinking, "please, not again. I can't wash anymore sheets this week."
With incontinence, the caregiver's primary goal should be to get an assessment from a physician, so you can help the person deal with expert recommendations. It shouldn't be to coax the person into adult diapers as a way of conveniently dealing avoiding the problem.
Before deciding on your own that diapers are the solution, it's always wise to get medical clarification of the problem. Many causes of incontinence are easily treatable, including urinary tract infections, prostate problems, medications, and consuming certain foods or drinks.