Rectal Dialysis?

Nope, won't work.

Epithelium of anal zone proper (the lowermost 8 cm or so) doesn't absorb or secrete anything at all, so there will be no exchange. The upper areas (up to the end of sigmoid) have excellent absorbing properties so the water from your solution will be absorbed, directly into hepatic circulation/inferior cava system.

Eons ago and in another land there was a method of keeping dehydrated person alive when no IV solutions/ equipment was available and PO was not an option. Thin rectal tube was placed in about 20 cm up there and approximately 1% salt, 5% sugar solution in whatever water was on hand was dripped in it up to 100 cc/h. Ridiculously, it worked.

If I had to choose, I'd totally go for sublingual dialysis rather than butt dialysis.

Y'all must be terrible nurses if this is how you show support and compassion (ever heard of that). My mom said it was a good idea and even put a picture I drew of it on the refrigerator! She said y'all are just being mean