It is prostate liquid (which is easy to confuss with precum). When it is a little white it is because it have also seminal vesicles one.I can sometimes squirt a clear liquid that I can only liken to a cum/precum mix. It is mostly likely to happen to me either during an extended edging session or from intense prostate stimulation. I see a really good masseur and part of his 'treatment' is centred on my prostate. He uses this rapid two finger movement inside me which nearly always generates a squirt. It's a really simple technique but he finds the spot every time. I have no control over the squirt, it just happens due to the sudden and very directed pressure he uses. It's always one of the highlights of the session.
You are a lucky guy: i don't know why it is no easy for most people find the area which trigger the squirting.