Aimee Glenister

OK permies, I ran the test myself.
After sipping rinsed seed-water, squinting at pictures of bagged grocery quince seeds, researching polysaccharides, sipping unrinsed seed-water...
I've concluded that when they talk about quince seeds as a palliative for sore throat and thickener (especially for quince-based desserts), they mean seeds that are either fresh and unwashed, or dried with that gel coating still on. It's not pectin--it's mostly a polysaccharide called glucuronoxylan-- but it's close enough to act like a pectin.
A small amount of water might be useful when separating the seeds from each other, but otherwise you want to preserve as much of that goo as possible.
Besides the sore throat remedy and thickening agent, other possible applications include wound-healing and hair-styling gel.
To make the throat remedy, you can either soak a Tablespoon of quince seeds in a cup of water overnight/a few hours at room temperature (no idea what would happen in the fridge--it might take longer), steep the same in boiling water (same ratio) for an unspecified amount of time, or boil the same together for 5 minutes (I haven't tried the boiling method yet).

citations:
https://food52.com/blog/5696-down-dirty-quince
http://www.mypersiankitchen.com/quince-seeds-persians-remedy-to-soar-throat-and-cough/

Chris: So looking back along my net history, I combined these two recipes-- https://www.allrecipes.com/recipe/268199/quince-apple-sauce/
and https://www.thepeppermillinc.com/recipes/3800/?srsltid=AfmBOopJEFwDxMxAnSBrq2OCGtrdl832s4V_kvPKY4m_T1oX24MxGVDB to get:

Quince-Applesauce:

Hand blender or other means to puree strongly recommended
Prep at least 1 quart jar and 1 pint jar with lids(I got well over a quart out of this while the recipe estimated 2 pints)
2 cups water
1 pound quinces — diced. (If not using a blender, core--and peel if that is your preference)  
½ lemon, quartered and sliced (the peel is great as long as it's organic)
1 pound apples — chopped (Again, peel and core if you must-- I don't)
~½ cup honey, depending on the sweetness of your apples
1/2 tsp ground allspice or cinnamon (pretty sure I went with allspice or half/half)
pinch of ground cloves

Prep the quinces and lemon. Combine water, diced quince, and lemon in a pot over medium heat (stainless steel or intact enamel--bringing quince into contact with a carbon steel knife makes very interesting smells). Bring to a boil, reduce heat, and simmer until softened, 8 to 10 minutes. Prep apples. Add chopped apples and simmer until all fruit is very soft, 10 to 15 minutes. Add spices. Simmer for 5 minutes to blend flavors. Add honey to taste. Puree in the pot with a hand blender, or allow to cool a bit before using a blender appliance.

There's a straining step in the All Recipes process that I skipped--I don't know if my recipe is therefore disqualified for canning because I didn't try--just heated the jars, packed them hot and let the lids pop before sticking them in the fridge.
The result is very low-waste, high-fiber, tart-sweet and luscious. Eat hot or cold but warm will give you the best of both worlds.

So we're processing quinces--I've done pie (4" tall going into the oven, 4" tall coming out!), a syrup-based sauce, apple-quince sauce (amazing! let me know if you want the recipe), Mogua-cha (Korean Quince Tea)...
In doing so I've run across several accounts of quince seeds as Persian folk medicine for sore throat, as well as a source of extra pectin--what's not clear to me is whether or not I should try to wash off that gooey (pectin?) coating they come out of the fruit with, or if they'll dry and keep safely with it on. Most of the people explaining the preparation of mucilage are using store-bought seeds and the ones using fresh seed aren't drying them. This is a dry wood-heat setting so humidity isn't a problem. Experience? Opinions?

Update:
Venison stew turned out tasty if not handsome.
I boiled the Canna roots separately for Fifty-five minutes.
They came out crisp. I cut them into inch-long rounds before adding them to everything else. It might have something to do with the fact that they've been in a fairly warm kitchen for the last week, or maybe Mom cut them smaller in the first place--but I don't know.
There's a picture of the cooking water around here somewhere--couldn't detect anything terrible in it. Maybe a little mineral but not metallic or muddy.
But yeah--00:55. Starting with cold water.

Very old posts here, but I'll add my two bits for people who come looking.
First--Are you sure you have the edible canna? Canna edulis/Canna indica. I guess I mean, what kind of yucky? Texture--fibrous, or just not what you are used to/were expecting? Taste--muddy/mineral(as the perfumers would say) bitter, bland, sour, turmeric or ginger-like flavors?
If you're getting unpleasant, ginger-like flavors, your canna species isn't quite right. They are indeed ginger relatives, as is the actual plant they make commercial arrowroot from, Maranta.
My mother boiled our roots--fairly certain they _are_ Canna edulis--for a good 45 minutes, with potatoes for comparison. I _think_ she peeled them first. They were bland, starchy, sporadically fibrous and a little watery (crisp, maybe?), but honestly I liked them better than cooked sunroot (Jerusalem artichoke). (Also no undo flatulence afterward. +.) Truly they are not just like potatoes--I've seen some people comparing them to taro--but I didn't find them offensive. I've also heard that there's pretty huge variability in stringiness between older and younger rhizomes.
She boiled them, hard. For _45 minutes_. I didn't think to taste their cooking water.
I'm going to have a go at them tonight--cook them separately and add them to a venison stew--I'm doing stock from meaty bones my uncle's buddy's didn't want.