Or you can try....
The best pressure sprayers are the larger ones used to spray insecticides from your local garden center.I'm just above you on coastal BC and I can tell you relying on the Black colour with your solar shower unit, or the black on the sprayer won't work that well.I used my smaller solar shower when back packing and it took for ever to become "luke warm." Instead I heated some water up on the stove and added it to the solar water, and didn't bother with waiting hours and hours for non-existent "warm" water.Personally go for the pressure sprayers and forget the black paint. The reason I recommend these is that when you add water, if its too hot, the solar bag can almost burn your hand. If you use the pressure sprayers, the plastic is thicker and you are less likely to burn yourself.Also when adding hot water from the stove, make sure to do a test "spray" before you shower in case the water you added is too hot.