Yes, don't just put the raw powder/crystals up there. Dissolve it in water and use an oral syringe or needle with the tip taken off to shoot the mixture up there. Also make sure to fully evacuate your bowels before hand.
It could make you have to shit really bad. Kinda like an enema. This doesn't happen too often though in my experience unless you're using too much water or redosing alot of times.
Summer, I've merged this into your other thread because I believe you'll find a good answer there. If you still had stool inside, the meth may not have been absorbed the way it should had it been somewhat empty.