I did misunderstand, I thought you were asking how to clean tons of gunk from the sub each week with fish in the tank.
If there is no fish in the tank, I would fill and drain the tank a few times, completely cleaning the substrate each time. If the sand is so full of gunk that you can't get it to look like normal, clean sand after a few cleanings, it might be better to just change it out for new sand. Then once it is cleaned, you are going to have to re-cycle the tank. You can use media from an established filter to skip this process. If you don't know about the nitrogen cycle, definitely read up on that, most important thing to know.
I find that the suction of the hose is dependent on the height. If the end of the hose is much lower than the tank the suction will be stronger. If the tank is low to the ground the suction won't be as strong. A wider tube on the hose can make the water flow faster as well.