Hi. We have a 24' travel trail that never moves as it is on our campsite full time. We visit every weekend and I am having troubles with blank tank odor. Since it is just 2 of us it seems a bit unusual. At the end of each visit I empty the black tank followed by the gray. When I am finished I fill up the blank tank with 4 to 5 gallons of water and then add the blue deodorizer (liquid) or sometimes the blue drop in packets. It does not seem to smell to much the first night but by the second night it has a very sour smell. I know it is not supposed to smell "good" but the smell goes throughout the trailer after flushing. I must be doing something wrong?