does your stomach still empty slowly for water? SN is absorbed very rapidly in the upper GI tract but i couldn't find any info for the lower GI tract, probably because it's all absorbed before it gets there. the timeline people experience with symptoms also implies that there's some absorption from the stomach itself, but i couldn't find anything in studies about that
Sodium nitrite (SN) will dissolve in water to form ions, Na+ and NO2-. This means sodium nitrite is an electrolyte.
While I can't speak to certain efficacies and how rectal administration would compare oral administration, what I can say is that the physiological role of the colon/large intestine in the digestive system is primarily to absorb water, water soluble vitamins, and electrolytes. So, it would most likely work to some degree. Small intestine absorbs most other things.
What you should consider though is that, as others have mentioned, it could be difficult to "hold" in your rectum. The rectum is a storage space for feces, and when it's full it generally wants to empty itself. It also may leak, as the anus is generally not water-tight. In normal digestion most moisture will obviously be absorbed by then, so it doesn't have to be. As of 2025 PPH recommends dissolving 25g SN in 50-100mL of water. This is not necessarily a large amount of fluid, but it's also not an inconsequential amount. It could be worth trying an enema of 50-100mL of just water, or water with some salt dissolved in it, to see how your body tolerates/responds to it.
My only real experience in this area is giving patients rectal suppositories. In pharmacology class, we were told that generally the longest it would take to see an effect is the same as with oral medications, but that the onset can be sooner. Essentially there is a greater "window" where you can expect to start seeing the effects of SN. This would be important to consider if you are taking other meds, because it could influence how the onsets overlap between them. Take this with a grain of salt though, because when we give meds they are generally capsules or tablets and in this case you would be giving yourself an aqueous solution/enema.
I would also maybe not advise taking other meds like metoclopramide, propanolol, or benzos intrarectally. To my knowledge most medications are absorbed in the small intestine, which is separated from the rectum by the colon. Your intestines do this thing called peristalsis where they rhythmically contract and push digestive contents in one direction, so backwards movement would probably not be the best. Rectal suppositories are also formulated differently from oral meds, so if you "boofed" an oral pill it could be absorbed and metabolized differently than what you might hope for. This would whether or not you get the desired effect, and how soon you would see it.