Hi, and welcome to DF.
The Wolf has no experience with CrystalMeth, but the method of rectal administration he knows from his opiate
use, it should be the same with methamphetamine
He would take the half of of one's normal dose and make a solution in not too much, let's say 5CC of Water and put it in a 5CC Syringe (without needle of course).
For Administration one should lie on one side and put the syringe a good way up (with the help of some vaseline) the rectum, 3-4" should be sufficient, then release the fluid slowly into the colon.
Before administration the rectum should be severely cleaned, an enema with 50-100CC of lukewarm water helps a lot, it is not essential, but the cleaner the mucosa is, the better the administered drug
can bathe the mucosa, the better the drug gets into the bloodstream.
To the amount of water to solve the drug: the less solution there is, the better the fluid can be held inside,but:
the more concentrated the fluid is the more it can hurt.
The Wolf is not sure if Methamphetamine hurts inside the anus, and how aggressive methamphetamine is to mucosa tissue, but he would be very cautiuos with it and use better more of a thinner solution and stay laid down some minutes longer than having the risk of a pain in the butt.