Esther,
I showed hubby your pics and design, and he is interested in trying to make one of these "thingies". However, our shop vac is only 6 HP, and when we tried vacuuming the bottom of the pond (regular hose on regular shop vac), it would not suck. Our pond bottom is about 30 inches deep.
So my question is, how much horse power does your shop vac have, and how deep is your pond again? I know you've posted that info on your pond depth before but my brain has lost too many brain cells and I can't remember!
We're trying to figure out if this idea is do-able with a 6 hp vac.
Another idea my hubby had was to buy a central vacuum motor and build something custom... seems to me a lot of money to spend on experimentation! I told him NO. I'm tired of failed, expensive experiments.