Actually the valve should be at about 4 o'clock, and give it a bit of a flick. So that any fluid in the valve can run out inside the tyre, and the fluid in the bottom can't reach the valve.
Another reason to use removable-core valves. I use presta and it's Schwalbe tubes for me as described at
http://www.tubelesswheels.com.
Reasons to use removable-core valves:
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[*] You can clean them (I like the vaseline tip, never heard that one!)[/*]
[*] You can replace the core if the stem snaps – much easier than re-doing the tyre + strip.[/*]
[*]If you're having trouble getting it up (ooh-er) in the first place, removing the valve can improve the rate of air ingress and get things seated. Then let the air out, careful to keep the tyre on the rim, replace the core and re-inflate.[/*]
[/list]
Cheers, al.