tman79: What is a good way to train my ass to take a large and long cock?

With toys. Use butt plugs and dildos regularly, gradually increasing the size as you can comfortably do so. Avoid all pain—if it hurts, stop and rest and resume more slowly.

Extreme length can be tricky—there is a bend at the end of the rectum which has to be temporarily straightened if the object is particularly long. The best way is with a flexible dildo and to gradually press up against the bend and back off repeatedly until it gives way painlessly and opens up. Then pass the dildo back and forth through it for a while as it relaxes further.

Always warm up with a butt plug and/or dildo before attempting penetration with the real penis, and be sure to be able to comfortably fit a toy the size of the penis before trying it for the first time for real.