Re a pond vacuum, I believe most if not all of the common wet and dry vac's with a pump suck water faster than the pump can dispose of the incoming water so the vacuum chamber gradually fills, I suppose you could couple an external pond pump to the vacuum chamber but there would be a bit of jiggery pokery involved in setting that up to work efficiently. You can also increase the size of the vacuum chamber, do a web search for "Floyd's pand vac" thats uses a 55gal barrel in the suction line. From what I hear the Oase pondvac Mk II automatically stops sucking and starts pumping when the vacuum chamber is full and then automatically switches back to sucking.
Some people, myself included, have made their own vac using a water pump or in my case a pond pump.
In my first attempt I put the pump inside a barrel, there is an inlet and an outlet to/from the barrel and the incoming flow is strained through a net bag tied around the inlet, to stop stones etc getting into the pump and to offer some chance of survival to any animal life sucked up. The problem with this is you have to get power to the pump, it is simpler to use an external pump out side the barrel. The outlet from the barrel connects to the inlet of the pump. It IS NOT self priming and the barrel has to be reinforced to with stand the crush. The nature of my reinforcing makes my barrel VERY heavy, too heavy to be easily moved so I made a MkII vacuum chamber with 4" sewer pipe. The pipe is strong enough to withstand the crush un aided but the bore was too small to be practical as the net bag fills to quickly and seals the bore. Mk III will be 6 or 8" sewer pipe if I can find end caps etc. If I can make such a vacuum camber then I can put the vacuum chamber and pump in the pond which should hopefully make it self priming. I spent a very frustrating day yesterday vacuuming my pond with the barrel head. To clear the obstruction I had to let air into the system which meant it had to be reprimed etc etc. There may have been a leaky suction joint which didnt help matters. When it was working it worked well and in a non congested pond it does a grand job.