Never had to combine vents in attic before. Always went straight out roof with one stack. Now i have 3 vents going up 3 walls i need to combine in attic. Any tricks to this? Is it as straight forward as it seems? Flip a sanitee over, make sure there's 1/4" pitch on the horizontal? Since i have 2 lines that need to come to the third one that goes out roof, how high above the joists would you put the first horizontal? A couple inches or a foot? I've never seen this done in person, just in books, that's why i'm asking. Anything i need to watch out for?

Thanks in advance.