Water and sewage weigh 8.333 lbs/gallon so even a full 10 gallon holding tank would weigh 83 lbs--plus the weight of the tank. Few owners have tanks as small as 10 gallons, so be prepared to be shocked when you find out what your holding tank weighs when it's full. Even a 5 gallon portapottie --portable or MSD--tank weighs close to 50 lbs when it's full. To compensate for the list this can cause, add an equal amount of weight to the other side. Some people use cement blocks...a few cases of beer would make re-balancing the load as needed a lot easier and more fun.
--Peggie