I was getting ready to post a question about duckbills until I saw Viper's list of questions. So here are my answers:
Yes, the pumps run. (2 heads).
Yes, pumps shut off.
Pumps run 30 to 40 seconds before shut off - could be a little less.
Hardly ever cycle on their own.
Yes, water will remain.
Yes, full evacuation.
Duckbills were replaced approximately 5 years ago.
Duckbills on Admiral's head are making a "weet weet weet" noise just before shutoff. So I figured it was time to replace. Then I figured might as well do both. Is it time?

I'm going to replace some of the hoses with hard plastic. Friend of mine told me I should wait till boat is in water so system can be thoroughly flushed. What does everyone think?

Question: Do anyone know where vacuum generator for forward head is located? Are generators located next to each other on starboard side of engine room near aft head holding tank? I have a waste & water schematic - if anybody wants one shoot me a PM with your email.