I premix one scoop with a gallon of water and dump in toilet. I then add two more gallons of water. I have never used any in my grey water tank, but you can if it gets an odor. If you go to the link in my top post there is a tab on the top of the page that is labelled "tank tips" it has the best advise I have seen for holding tanks. I have a 40 gallon each black and grey tanks and have never had a problem with happy camper. It doesn't try to mask the smell like other chemicals, it eliminates them.
Congratulations on your new trailer.