i don't know the answer, except i wonder whether a http proxy like privoxy is really necessary for the app you're using.
if it's a web browser, you should be using torbrowser, which doesn't need a http proxy. or anyway, most other browsers can use a SOCKS proxy (tor) directly
if it's not a web browser, well, curl for example can use a SOCKS proxy directly.
and there's torsocks to torify other apps that don't support SOCKS