The sink rise is from white crane or similar. The purpose is power generation without much movement (i.e. without body momentum), required because of the strategy used in this kind of system. I don't see how using it in the VT system is optimal in terms of the strategies employed, or how it would mesh in terms of body mechanics already there.
I think Alan shows these things being effective in chi sau, and if you approach chi sau as a directly applicable thing then these ideas might work for you.
I don't think most white crane practitioners would see the sink rise as internal, per se. Personally I don't really understand what internal means, and how it is different to "external"?
I really have no idea why you just keep guessing and making statements referring to what I do when you posts all clearly should you do not understand it at all.