Yes, enema and tentacle isnt an ordinary every day thing, but i think the idea behind it is roleplay. The other bound and or restricted and being forced. Or totally helpless in a "beast" his lust and cravings. Of course im aware tentacle is fiction, but its nice to fantasize. Roleplay in real life should always be done with approval from both sides, and its wise to have a secret word, which you can say if its really going too far.
NOTE: Dont do enemas at home! Its a great risk for your own health. But if you want to try, i urge you to read some enema guides which are found quite easely on the internet.