A few grams of sodium chloride is not going to destroy your plumbing or your landscaping. Your plumbing is in daily contact with sodium chloride from the food we eat, the sodium chloride that is in municipal water supplies, and it is a common substance to be found outdoors as well, including soil.

You don’t want to put kilograms of it in your garden, but this device is not consuming anywhere close to that amount of salt. It holds about the quantity of a salt shaker of salt, and can be fired 80 times from that amount.

Well that's where the Roomba carrying a tray of margaritas comes in.

If one could be made to shoot fine sand, it could be used outside I bet.