Hi!
I'd like to add a little variation on 5 - adult duck bedding.
It really depends on their environment. My ten runners have about 60 sf of shelter for overnight. Their outdoor shelter (spring, summer, fall) has about a foot and a half of pine shavings. Daily I stir it with a one inch diameter staff (a rake handle works, too), to fluff it up. On top of that I have a couple of inches of dry straw, which I push out of the way before stirring the shavings. The straw gets changed out a couple of times a week. The shavings can stay in there for months.
There is no food or water in their outdoor shelter - so it doesn't get wet and gummy and nasty. Also, eggs laid in this duck house are quite clean because the bedding is clean.
Wintertime, they are in the walkout basement. Daily I pull damp straw out from around their watering station (I have a splash catcher but when they leave the waterer for their food, they dribble). I replace that. The rest of the straw can go several days, sometimes a few weeks, depending on the weather (how long they have to stay in during nasty storms, wet days, etc.). In areas that tend to get damp, I put compressed sawdust pellets down before putting the straw on top - that absorbs moisture quite well.
One benefit of this system is that the used straw, enriched with duck fertilizer, gets moved onto garden beds.
Take good care of those ducks!