Only the obvious - the bucket of salt water needs to be at a higher level than the nitrate filter for you to start it syphoning. It takes a fair bit of strength in cheek muscles to get it started (I was OK as I used to play Sax )
I have used this for about a year now recharging roughly every 2-3 month's.
when I recharge it, its fairly easy. Like fish lady said have the bucket higher with salt in and have everything else lower. Don't follow the diagram you get though, have the filter also flowing straight down rather than upside down. Once it starts it is really slow to recharge but it gets there. Normally recharges in about 2 hours
Rob 5 Cherry Barbs, 1 Steel Blue Killifish, 1 pair of apistogrammers and 2 Bolivian Rams