The filler has a tapered fitting that accommodates 5/16, 3/8 and 1/2 siphon hoses. To use, simply attach a siphon hose to the spigot on the bottling bucket & filler unit, turn the spigot on, push the button on the filler & the filling begins! When the bottle is full, the unit automatically shuts off, supposedly. The rubber piece that goes into the bottle can be moved to adjust the fill level but I found it not necessary. The nut on the top of the unit allows regulation of the flow. The nut broke off after two uses but not necessary anyway. Be prepared to overflow at least once in every filling session. When you want to start the filling, you push the top part down like a pen and flow begins. Auto shut off doesn't work everytime so you must manually stop the flow by pressing two opposing release buttons on the side. It doesn't release sometimes so flow continues. Be prepared to mop some beer from the floor. I find the position off the flow stop pins and hose connector rather awkward. You cannot get a nice full grip in your hand but you have to hold it with finger tips. Overall, it works fine if you expect the unexpected and be ready for it.
Edit: Today I bottled using this product again and threw it out once I was finished with it. It gets stuck open and overflows with almost every bottle now. You have to pull the top portion out with your other hand otherwise doesn't pop up to shut the flow down. As it stands right now, I cannot recommend this product based on my limited experience.