You have to make sure your asshole/rectum is clean. If you're well-cleaned, and if you're well-lubed, the possibilities are endless! Your asshole will accept cocks or dildos of very big sizes. If you have any damage to your asshole, such as fissures or hemorrhoids, go to a proctologist and have that fixed. Always start small, with a finger or a small dildo -- and then take something bigger. Have fun pretty boy!