That method used to work for my bathroom sink (run water for a min then stop), but now I have to use the kitchen sink so I just run it out my front door. My bushes enjoy the used tank water a lot and it doesn't go down the drain. For some reason I get almost no suction if it has to go back up in any way. But that's the way my house is laid out. I guess if that method worked you could run water to get a powerful suction to grab the gravel vac then if you needed more than the 10% that normally takes (well on my 29 its that quick) then I just put it in the corner where no fish are and leave it be for like 5 min then switch the flow after conditioning.
Either way you do it, it's easier to fill that way. On average my water changes used to take me 2 hour for a 5.5, 10, 29 and 46 gallon. Now it takes like 25 min if I hustle or there isn't much vacumming to do. And I don't have to lift 5 gallon buckets up 4-5 feet to the top of my 46 and 29 which is always a plus
BTW The head on that thing can be junk and is the weak spot. It's the part right below the faucet (it's a cone inside the green l bend part) .. if you EVER need to replace it.. this is identical and it's what I used for my home made one. I got it for 4.99 from ace hardware