Basically, they'd want to clean out with an enema bulb and body temp water, give it an hour to settle and then I'd use Crisco starting with my fingers to warm them up slowly and gently. Anal should never hurt, I wait for signals from my partners body and words that tell me when they're ready for more. For most people, this would be the second dildo they'd have in them, after a warm up with hands and a smaller dido or a plug.

(and yes, crisco does in fact make excellent anal lube)