I copied down their ingredients from the menu, but I'm not 100% sure of the amounts...but, this is how I make it.

RED LOBSTER MANGO MAI TAI

2 oz. Malibu Mango Rum
1 oz. Dark Rum (not in their ingredient list)
1 oz. Triple Sec
1 oz. Grenadine
Equal amounts of orange and pineapple juice (about a 2 sec. pour of each).

Pour all ingredients over ice and shake for a few seconds, then pour into a pint glass.

I usually end up with a little more than a pint glass full of the Mai Tai. I guess it all depends on how much juice you use. Anyway, like I said, not exactly sure how they do it, but I like mine...give it a shot and let me know what you think ;).