Hi,
I've been fisted by women. Their hands are smaller, but I've been trying to find a guy to try to get in me too.
Getting fisted properly is awesome, finding someone you can relax enough with is the hard part. Being totally relaxed, eager, and ready is critical.
Being ready...clean, most important thing. If you don't have, get an enema bag (hot water bottle), or plumb a shower shot type unit to your shower.
I smoke pot, helps relax greatly, I also use poppers throughout the event.
I get in the shower, wash my ass real good, then fill the bag all the way. Use very warm, but not hot out cold water so you don't burn or cramp. A 1/4 teaspoon of table salt in each bag is reported to help keep you from drying out inside.
I apply a small bit of Vaseline to my hole with my finger...this is where the good feelings start...
I then slide the nozzle of the bag in my ass.
Release the clamp and let the warm water fill me up...as the bag nears empty, I pull the nozzle and wash it off. I then take a couple hits of the poppers, it relaxes you inside and lets the water get deep. I then refill the bag, and really fill myself up...
I hold this a long as I can, taking that time to fully shower. When its been 10 minutes or so, or I can't take it, I hit the toilet and let go. The emptying can take 20 minutes.