Rectal infusion is definitely a thing. Take a camel back, cut the mouthpiece off and shove it up in there about an inch. Put whatever fluid you have for rehydration. However do not use just water. You will give them an enema which has the opposite effect of what you’re attempting. Make sure whatever fluid you use has sodium in it.
Now a word about dehydration. The biggest treatment for dehydration? Prevention. DRINK. WATER.
Gatorade is cool but you get most (like 90%) of your electrolytes from food. If you’re only going to eat part of an MRE, eat the main meal and the cheese or peanut butter. They both have sodium and the cheese and peanut butter have needed protein for energy. Dehydration is so preventable it isn’t funny. If you want a cheap oral rehydration salt take a cup of water, a salt packet, (flavoring is optional) and drink that daily if you’re in a very hot environment and sweating a lot. We had guys do that last August when we were in El Paso and the ones that did that had less issues than the ones that didn’t.
Drink water
Drink water
Drink water
Drink fucking water.