I wrote a more thorough Amazon review for this product, but there was a glitch and it got deleted somehow. I don't have the patience or enthusiasm to re-write that whole thing, so instead I am trying again with just some basic facts and considerations.- This is an electrically powered fuel transfer pump. It is powered only from "AA" cells (batteries), and can work with just two of those, but for best pumping power & battery life you can install four of them. For year-round use, I suggest installing Lithium type cells, such as the Energizer Ultimate Lithium brand, because these a tolerate wide temperature range better than alkaline types, and don't have the problem with leakage that unattended alkaline cells do.- The battery compartment is the center piece of the assembly, and contains the cells/batteries, the power ON and OFF pushbuttons, a discharge nozzle storage chamber/dock, and it attaches to the opening on most common North American brands of 1 gallon and 5 gallon plastic fuel cans. Three adapters are included with the product; one of them fits my "Blitz" brand 1 and 5 gallon cans, another of them fit all of my "No Spill" brand cans...I don't know which brand(s) the third one might fit (maybe the Scepter brand?). You find the adapter that fits your can(s) and screw it onto the opening of the can, then screw the battery compartment's threaded fitting onto the adapter.- A flexible intake hose extends from the battery compartment, through its threaded fitting and the adapter, into the fuel can. The actual pump is permanently attached to the end of the intake hose, and is supposed to either hang inside the can or lay on the inside bottom of the can. The flexibility of the hose and the size of the pump housing is such that it will lay on the bottom, more or less on its side, if you are using a 5 gallon can. On a 1 gallon can, the pump and hose will have to fit however it can, but might not have the pump inlet right at the can's bottom, limiting how far down you can pump it empty. On a can larger than 5 gallons, the pump might just hang at the end of the intake hose, without touching the bottom of the can, so there might be some unpumped fuel remaining.- The electrical power for the pump gets to it (from the battery compartment) via a fuel-safe cable that is inside the intake hose. Regardless of how many batteries you install, the maximum voltage in this cable and at the pump is 3V. It is supposed to be safe to have the pump permanently installed on a fuel can and operated as-needed.- Unlike most modern plastic fuel cans, which have a ratchet-type mechanism to prevent accidental unscrewing of the nozzle (and this feature is also supposed to make the cans "child proof"), the threaded fitting and the can adapters of this product do NOT have any such feature. Take care where you locate the fuel tank(s)/can(s) being used with this pump!- The pumped fuel exits the battery compartment via another hose (the discharge hose) which is 34" inches long. Some of the sales text associated with this product suggests that this hose is elastic, or can accordion or telescope to be shorter or longer; I did not find that to be true.....it is 34" inches long, period.- At the end of the discharge hose is a 4" long discharge nozzle, and this is the part you insert into the opening of the fuel container you are trying to send fuel to. This can be the fuel tank opening of an automobile, the top opening of the fuel tank on a lawn mower, snowblower, small garden tractor/riding lawnmower, etc. The nozzle does not have any kind of valve, and does not have any kind of manual control for fueling (as does, for example, the fuel nozzle that gas station pumps have on their hoses)...it is just a 4" long plastic tube. There is a plastic clip molded to the side of this discharge nozzle, and it is intended to hook onto the lip of automobile fuel tank openings, or to the threads on the fuel tank openings on tanks of lawn mowers, etc; so that the nozzle does not accidentally fall out of the tank/can openings during fuel transfer. Pressing the end of the plastic clip springs it up just enough to allow it to disengage whatever it was hooked onto.- Inside the end of the discharge nozzle is some kind of electronic sensor; I think it is just a tiny electrical probe that detects the conductivity of the fuel when it comes into contact. It is connected to the battery compartment via a able that, like the intake hose, runs inside the discharge hose. When fuel touches or comes close to that sensor, it signals the battery compartment circuit to stop the pump. Both the ON and OFF pushbuttons are momentary types, so this sensor acts like a secondary OFF button. In my experiments, the sensor works quickly and well, but see my caveat below. When you are not pumping fuel, the discharge nozzle docks into a tubular chamber on the battery compartment, and a raised plastic ring at the opening of the chamber gives the nozzle's clip something to hook onto.- There seems to be nothing about the design of this product to prevent siphoning. The included operator's manual advises to always have the source tank/can at about the same level as the destination tank/can. This does not mean that the pump cannot push fuel up to higher levels; indeed, it can raise fuel up the discharge hose even if that hose is held straight up vertically from the fuel can that the pump is inside of. This caution appears to be to minimize siphoning. Even if there IS some kind of anti-siphon feature that I missed, there is still the issue of "what happens to all the fuel that is already in the discharge hose when you turn the pump off" (either by the OFF button on the battery compartment, or automatically when the sensor detects fuel at its end)? The answer is: if the discharge hose is horizontal, or if it is sloping upwards from the tank/can where the pump is, the fuel will either stay in the hose or will run backwards into the pump's tank/can. BUT, if the discharge hose is sloping downwards, as soon as the pump is stopped all the fuel in that hose will immediately run out through the discharge nozzle. EXAMPLE: I had a 5 gallon gas can, with the pump inside, sitting on a shelf 2 feet above the floor of my garage. The discharge nozzle was clipped onto the opening of the fuel tank of my walk-behind lawn mower (which was lower than the gas can where the pump was). When the mower's tank got full, the sensor immediately stopped the pump, and then all the fuel in that 38" (34" hose + 4" nozzle) of hose (roughly 1/2" inner diameter) ran out into the lawn mower tank, overfilling it and all that volume of gas ended up on the garage floor. Since that happened in about a second, I did not have time to unclip the nozzle and raise it up above the level of the gas can, which would have stopped the flow. It is better to use this product such that it is pumping at least a little bit higher than the level of where the pump itself is located.- This product seems to me to be of decent quality. No part of it seemed cheaply made. But I do wonder about how well it will hold up over time.- I recommend always rising the discharge nozzle above the pump's tank/can so that all fuel runs back into that tank/can, rather than leaving it inside the hose(s). And also always store the product with the discharge nozzle docked into the battery compartment chamber intended for this purpose, because this will eliminate any chance of siphoning causing a fuel spill while not attended. And this is a "pretty" looking product, with attractive red and green buttons that a child might want to push...if they push the ON button while the discharge nozzle is docked in its chamber in the battery compartment, as soon as fuel starts coming out of the end of the nozzle, the sensor SHOULD immediately shut the pump off again. But best to locate this away from where any children will be while unattended.