Best way to clean dust off focusing screen of 5D3?

[switters]

There's a large, black speck of dust in the upper-right when I look through the viewfinder of my 5D3. I suspect (but don't know for sure) that it's on the focusing screen and not in the viewfinder itself.

Unfortunately, I'm pretty OCD about this stuff and I know that speck will drive me crazy even though it won't affect the pictures. Some folks here and elsewhere have described using a blower to successfully clear the dust. (I do have a Giotto Rocket Blower.) Can someone describe that procedure — especially with an eye toward minimizing the chances of introducing new dust?

[mw]

I have the same exact thing, except it's in the upper left. Drives me crazy. Tried to use the rocket blower, but no luck. I am thinking of sending it in to the Canon Service Center, but not sure if it's worth a couple of hundred dollars getting it done.

[Mt Spokane Photography]

Its likely not actually on the focus screen, but above it.  If it will not blow off with a gentle puff from a rocket blower, send it to Caon for cleaning if it really causes you a issue..
Do not touch the screen or mirror, that will ruin the screen, and might mess up the mirror as well.
 

[switters]

I'm in luck: a few puffs of the rocket blower removed it. I think it was on the mirror.

[Sporgon]

If the dust looks blurred then it's on the outside of the screen and can be blown off as yours must have been.

If the dust looks sharp it's on the inside, either on the screen or bottom of the prism. If your camera doesn't have an inter changeable screen then you are stuck. This is one of the reasons I much prefer a camera that has user interchangeable screens.

I wouldn't try dusting the screen with a lens brush to remove dust as you can charge the screen with static and it will then become a dust magnet !

[Mt Spokane Photography]

I'm in luck: a few puffs of the rocket blower removed it. I think it was on the mirror.

Thats great, I'm glad it wasn't one of those tough ones.

[spinworkxroy]

I have the same thing on the upper left..
I even tried using the jet air guns to spray it…actually, that's what i do after every shoot..i know i'm not supposed to use compressed air to spray into the sensor, but i do…still can't get rid of that speck…it's in the viewfinder..which mean i can only hope one day it will drop on its own

[awinphoto]

Just be careful... I had dust that was stuck good... was too aggressive trying to get it off and f*cked the screen up... They are pesky buggers

[TexPhoto]

A crazy thought i had is this: Russian 35mm cameras like the Kiev (a whole brand of camera) used the Nikon F mount. Essentially they copied Nikon so well the lenses and bodies were interchangeable. 

I wonder if in some effort to stay compatible with Russian Gear, they chose to go with Nikon.