you're welcome.
I do have a Eheim gravelvac but nothing beats the old soda bottle.
You just have to find out what size of bottle to use and how far you cut off the bottom to get the best result.
It has to make the gravel swirl and the poo extracted without the gravel getting sucked out as well.
1/2 liter bottle works best for me.
I started with the bottle because i was fed up with moving the rocks everytime i cleaned the gravel, plus i used to stir up a lot of mess without catching it and made my tank look like a "Snowglobe".
nowadays after a waterchange the tank looks clean right away!