I understood recently that a wet/dry pump (a "shop vac", that is, though not necessarily from that brand) functions by creating a vacuum in an air-tight chamber. The vacuum sucks in anything near the hose, whether it's wet or dry.
I've also seen one manufacturer advertise that some of the wet/dry vacs in their product line can function as a wet pump (in addition to being a wet/dry pump).
I like the idea of using one tool for both functions (in terms of both storage space economy and pocket economy). I'd be using the wet/dry vac to clean the garage floor (maybe 4-6 times a year) and the wet pump function to empty the water on top of a pool cover (somewhere from 250 to 500 gallons, once or twice a year).
Is it indeed the case that a wet/dry vac that can double as a wet pump is capable of continuously pumping? Any wet/dry vac can be used as a 2-stage wet pump (fill, empty, repeat), but doing that 25-100 times in a row is not amusing. Did I understand correctly and some wet/dry pumps can indeed continuously pump water?
I would be perfectly fine with a device that sucks water from the hose, but then allows that water to drain via a syphon from a garden hose, just so long as this process does not need user intervention until it's done.
Best Answer
There are two solutions:
Wet/dry "Pump" Vac
Look for a wet/dry vac that is labeled "pump" (the manufacturer will likely draw a nice hose with fresh water prominently on the box).
Such wet/dry vacs have a built-in water pump. One model on the market looks like this:
Universal Pump for Wet/Dry Vacuums
These are add-ons to your wet/dry vacs. Your vac must have a downspout for this option to work. One model on the market looks like this:
Neither of these options will allow continuous pumping.
You cannot continuously pump out with the first option because the wet vac will be faster (more powerful motor, 1 1/2" to 2" hose) than the water pump (5/8" garden hose, pump handling just water rather than an air/water mixture).
You will need to pull the hose out of the body of water when the tank is full. Force the power button down to override the shut-off feature for 15 seconds. The water pump will then continue pumping out (at 350 gallons per minute) until the tank is empty. Repeat.
You cannot continuously pump with the second option. You will have to attend to the two pumps. Fill the tank with the wet vac. Turn off. Empty the tank with the water pump. Turn off. Repeat.