Should I leave the water bottle tip open or shut while in the cage? When I'm riding (all road, never trails) I leave the tip on my water bottle shut. When I take a drink, I pull the tip open with my teeth, squirt some water, and then bump it against my slightly-opened teeth to shut the tip again.

I do it because the tip of my bottle will often get dirty, and I'll have to wipe it off with my shirt before drinking. If I leave it open grime would get inside the tip of the bottle.

It is a bit tedious, but I'm now used to it. Is this standard practice?
To quote David Richerby: You're over-thinking this.

Most people close their bottles most of the time.

I'm not one to worry about a little "gunk", but I close my bottle more than half the time. I almost never wipe it (heh, I almost never wash it :-)

Not fanatical about it though. If I'm taking a quick swig before a corner then I'll just jamb the bottle back, whether the top's open or closed, before I get to the corner.

That can happen a lot, because I drink a little, often.