Hiya,
I don't think you are planning to get anything that is likely to breed on you. The "livebearers" are generally the problems for that. Egg-layers, (what you are looking at) may lay eggs, but they usually get eaten before they hatch, particularly in such a small tank.
Here's how I use my gravel vac. It's the same kind you have:
1. Put a fishtank-use-only bucket on the floor by the tank. (Fish are very sensitive to soaps and cleaning products, so buy a shiny new bucket, rinse it really well in straight tap water, and then never use it for anything other than your tank.
2. Dip the gravel vac into the full tank, so that the wide end and the long tube fill up with water. Pull it out of the tank. You now have a gravel vac full of water.
3. If there are any big air bubbles in the tube part they can disrupt your vacuuming. Put your thumb over the opening of the long tube so no water squirts out and carefully raise and lower one end of the gravel vac until any big air bubbles travel to one end of the vac and burst. Hint: air rises!
4. Keeping your thumb over the long tube end, hold that end low down, and over the bucket on the floor. Insert the wide end of the vac in the tank so that it is completely under water. Take your thumb off the other end. Water should start flowing into the bucket. If it doesn't, you have a big air bubble, or you didn't get the wide end of the vac completely under water before you took your thumb away, or your bucket isn't low enough compared to the height of your tank. (That's one reason tanks go on stands instead of just on the floor).
5. Use one hand to keep the tube in the bucket so you don't splash water everywhere. Use the other hand to guide the vacuuming end gently over the gravel. Gravel will be sucked into the vac, but is too heavy to actually go up the tube. The dirt will go up the tube.
6. When your bucket is almost full, remove the vacuum end from the tank. Let the last of the water drip from the tube into the bucket.
7. Empty the bucket into your houseplants or on the lawn. Fish poop is great fertilizer.
8. Rinse bucket in sink if neccessary. Refill with water that is the same temperature as the tank. You can float your aquarium thermometer in the bucket while you refill it to be sure that you get the temperature right.
9. Add dechlorinator to the bucket.
10. Pour the clean, dechlorinated water into your tank. Use your free hand to break the stream of water, so that it doesn't wash your gravel and decorations all over the tank. Depending on how tall your tank is, how tall you are, and how big your bucket is, it may be helpful to have a buddy be the extra hand for this until you have practiced a bit.
If you want so practice without bothering your fish, fill a big mixing bowl with water and put it on your kitchen counter (warning, be careful of dish-soap residue contaminating your fish tank equipment!) and use your gravel vac to empty the water into your fish bucket, or a second bowl sitting on the floor.