THE SMELL IS FROM STAGNANT WATER IN YOUR TANKS AND LINES WHEN THEY ARE NOT DRAINED. THETFORD MAKES A SANITZER KIT THAT WORKS GREAT. AFTER YOU CLEAN THE WATER SYSTEM,DRAIN THE SUPPLY AND WATER HEATER TANKS. BY-PASS THE WATER HEATER, MOST CAMPERS HAVE THEM BUILT IN, THEN BLOW OUT THE LINES.IF MY RV IS NOT GOING TO BE USED FOR MORE THAN THREE DAYS, I DO THE ABOVE PROCEDURE, IT ONLY TAKES FIVE MINUTES. IT HAS BEEN YEARS SINCE MY WIFE HAS HAD TO COMPLAIN ABOUT SMELLY WATER. SHE NOW HAS MOVED ONTO CLOSET SPACE.