Ok. Just got that Sawyer's wonder at the local REI. Well, it works nicely. You need just fully extend the plunger, apply the suction cap over the wound, and depress it completely to activate the spring inside, which in turn will produce the force on an internal piston. So you don't need to apply force anymore, just leave it stuck to the skin and do its sucking job for 2-3 minutes. Pull the plunger to release the vacuum. Repeat 4-5 times, wiping the extracted liquids. 15 min total. All this is according to the instruction manual.

Funny enough - the Sawyer's suction caps fit perfectly the standard disposable plastic 60ml syringe (big one, just a little larger than the Sawyer), which I took at work for comparison as promised. The test was simple. I've applied the Sawer to some place on my thigh, activated it and watched the skin bulge growing. Then, using the same Sawyer cap attached to the syringe I've pulled the plunger. Ouch! I've pulled too hard! The sucking power of the syringe is much stronger! But yes, you have to continuously stretch your muscles for 2-3 min. An you'll need both hands to do the job. Yes, I was able to make a much nicer bulge with the syringe.

Conclusion? Nice suction caps for my syringe, some fascinating survival reading about venomous species, cute yellow box, and a disposable shaving razor as a bonus (an ancient single bladed though)...

By the way. The manual says the mouth sucking is only dangerous if you have an open wound in your mouth.