For purposes of collecting a dry, relatively pristine stool sample at home, is there any way to get the bowl to not fill up with water again after flushing but still be able to flush stuff out once desired?
Turn off the water supply to the toilet and flush it, do ya thing, then turn the water back on until the tank fills, then flush at will.
Put a plastic bag in the bowl. Makes harvesting your treasure easier, as well.
Use either a potty (like for kids), a bag, newspaper, plastic wrap, a small bowl, or something. Don’t let your sample touch the inside of the toilet bowl.
~Max
Not quite the answer to your question but I had to give a stool sample to the doc once and he recommended using one of those pie tin things to collect it initially before putting it in the testing container or whatever, worked pretty well.
If you’re really in a bind, I could send you some.
He said “pristine”. I can just imagine what sort of interesting chemistry might be found in some of yours. 
Sheeeeiiiiit, man. 
Use a bucket?
Every time I’ve needed to collect a stool sample at home, the kit included a paper shield that you float on top of the water and then take your sample from the dry paper.
Squat way down like you are about to use a Middle Eastern toilet or a cathole in the woods, that way you can see what you are doing, and pinch off a small quantity into your pie tin, or directly into the sample container if your aim is good. Don’t bother with the regular throne (except for the rest)
I bought a cheap plastic bowl from The Dollar Store.
- Turn off water supply to toilet
- Flush to drain existing water. Some water will remain at bottom.
- Place bowl in toilet
- Sit & shit
- Pull up pants
- Use a throwaway something or other to select & scoop a portion of shit
- Place portion of shit in strong plastic bag, such as freezer bag. You don’t want it breaking.
- Discard bowl. Alternatively, gift it to someone you don’t like.
- Turn water back on.
- TIP! If you see a section of your poop that doesn’t look normal, either avoid scooping that section or try again in a day or 2. A problematic selection of poop will result in your going for further testing, such as a colonoscopy. This is someting to be avoided if possible.
Did you leave out a step between “Sit & Shit” and “Pull up Pants”? If not I don’t want to see your laundry basket.
Healthy eating. My own stool are perfect. They are huge and have no more odor than a hot biscuit.
I don’t know what your goal is here. If you’re trying to avoid finding out that you have cancer, that might make sense. But I think the idea is to find out if there’s a problem.
If you need a pristine stool why poo in a toilet?
Put a garbage bag on the ground (or plastic wrap), squat and do your thing.
Voila…pristine stool sample. Wrap it up and take it in.
Squatting to poo is actually super common and a better way to poo so it should be no trouble.
Made me think of the Wire. And laugh.
I used a sheet of plastic wrap across the bowl. For my sample (hemoccult) I just needed a small amount, so I scooped then flushed the rest down.
Now that there have been some excellent replies to the question, I feel that the following link is appropriate…