This is extremely simple, fast, easy to make and works far better than those sold by office supply stores.
Step 1: Items Needed
Find a water bottle and something to poke a pin hole in the cap. Push pin will work best. This is all you will need to make this Instructable. (Oh and some water of course) ;-))
Step 2: Make Tiny Pin Hole
Make a tiny sized pin hole in the center of the cap. Be careful to not make the pin hole too big or you will have soggy envelopes. Start off with a tiny pin hole, test it, and adjust pin hole size as needed.
Step 3: Assemble
Put water in bottle (about half full), and place cap back on bottle. Then turn bottle over and give about one or two gentle squeezes as you glide over sealant on envelope.
Step 4: Finished Results
You should have just the right amount of fluid to now seal the envelope. I personally like the smaller (8 oz) bottles cause they are much easier to work with than the lager ones.
Make one for your secretary or the mail person it will save their tongue.