Holes are for fucking and since strait men don't get fucked, the manhole makes the distinction clear. Derogatory towards gays? I don't know. It's just a word, but words are fun.
2. mmmm, sweet male anus. yummy!
"oooo, you sexy manhole, you!" - good for getting the romance started.
"You actin like a bitch. Maybe you need a cock in your manhole." - shit talking
"I wanna open up your manhole and have an adventure in your sewers." - gay sexy talk
In general, a very versatile word, good for adding color to your speech.
2. Male orifice, typically the mouth but also could refer to the anus or butthole.
"Dude you want to keep your manhole covered or someone's gonna cap your ass."
Nick: Yea, her dumbass didn't know that a manhole was hot....
Darbi: haha yeah! The way she screamed made me want to pee my pants!
Nic: I don't know man, i stole your phone yesterday and was looking at those nude pics she sent you. To be honest, thats one manhole i wouldn't venture into.