I went 3/8th... but remember I am deleting my power steering, the pipe is a vent to link the 2 connections up. Basically I am doing a DIY version of: https://eaaengineering.com/products/mk4-golfjetta-gas-diesel-bew-de-power-steering-conversion Granted its not as pretty, but all in a lot less cost than the $89 + postage from trumpville and then HMRC taking a chunk as well  If I don't like manual I can put it back - will try it in stages, initially drained system for some mixed