A syringe and a cotton ball will do two things, first is clean your merc so it will pick up gold better. gets rid of the surface impurities. You basically strain the merc. Put the cotton ball in the syringe, add the merc, then plunge it.
Same thing when recovering your gold, it will be in a ball trapped in the cotton, while the clean merc comes out the other end. Use a dilute solution of nitric acid to remove the rest of the merc from your gold, and you are ready to melt it or whatever.
Oh yeah, and a neat trick. To get the merc that went into soultion in the nitric back, simply mix up a little baking soda/water and add the acid solution to it. (neutralizing the acid here) Then drop a clean piece of copper in and the merc will come out of solution and adhere to the copper.
I have heard this, but haven't tried it.... someone told me that if you put dirty mercury in a bottle and add some dry baking soda, cap it off and give it a good shake, the soda will "scrub" the impurities off the surface of the merc, allowing it to pick up gold better.