All this work to get a syphon going, and using your mouth! That just turned my stomach. 8O
OK, what I use is a syphon bell. You put it on the end of the tube (opposite side as the gravel vac) and it starts the syphon as you pump on the plastic valve (kind of like a turkey baster). I purchased mine from Big Al's but I'm sure they sell them all over the place (probably Home Depot sells them too in a plumbing section or so). I'll see if I can find the one on Big Al's and post a link.
No mess, no fish poop in your mouth :?, and its cheap.
As for the gravel vac syphoning too much water too quickly, you might need a smaller one. I had originally bought the large vac (probably 2.5" in diameter) and it sucked out water so quickly I could never get it around the tank to get all the gunk.
I disconnected the gravel vac and now use just the tubing as the vac. What this does is create a much stronger suction so that you can quickly move around the tank and nothing sits at the bottom.
If it is still flowing too fast, raise the tubing off the ground that is going into the bucket. The syphon effect is directly related to the height difference between your tank and the bucket your filling. So if you have the bucket on the floor and the tank on a tank stand (like I do), it will go REALLY fast. Put a box or something under the bucket (or just CAREFULLY aim into the bucket while holding the tube higher). This should give you enough time to easily get a good gravel vac without sucking out more than 50% of the water.
justin
EDIT: Here I found it:
http://www.bigalsonline.com/catalog/product.xml?product_id=19361;category_id=2001;pcid1=3347;pcid2=