"special sauce" in any given poll, because you have to make educated guesses about the universe you expect to eventually show up on election day. But what I think PPP usually does, and what the pollsters I most respect tend to do, is weight to the census for a given geography and let the interviewed tell you the rest. Everything else is a step above dart throwing.
Weighting by party ID is highly controversial because party ID is an attitude and not a demographic category. People can and do change their minds about what party they identify with.