how to gravel vac without a mess
get a gravel vac, a clean bucket (large enough to handle your water change amount). Have a towel ready just in case.
Fill the large syphon part of your assembled gravel vac by holding it partly below the surface until it fills without with aquarium water and while holding your finger almost completely covering the other tube end of your vac. (both ends are at this point at equal level). Now here it goes.
Slowly (!) lift up the big end out of the water and you will feel air pushing out the other end past your finger. Watch until the water almost reaches your finger blocking the tube. Be fast and block off the tube now, or you will have a mess.
Now keep the end blocked and dip your large end back into the aquarium opening pointing higher up until air is all out and the big end entirely filled with water.
Now tilt the big opening down to your gravel. Make sure no fish are around the immediate area,
guide your hand holding the other end of the tube still blocked over the bucket.
Check for fish again and then release your finger from the tube. Water will start flowing until you lift the big end out of the water. (Tip: check your bucket every once in a while, lol).
Now you can either just suck out the water or "dust" the top of your gravel or "deep-clean" by pushing the big part into the gravel.
If you only do small water changes, you can pinch the tube to stop the flow, move to the next area, release the tube and water will be sucked again, and so on.