I have read with interest the threads and solutions for sagging fresh water tanks but not much has been posted about sagging grey and black water tanks. These tanks are narrower (25" vs. 37") than the fresh water tank but they still have some sagging. The hope is that the bottoms will rise back up when the weight of the water reduces as they are drained. I'm not convinced that happens because my tank bottoms are not flat when empty. The bottoms are angled downward to the corner of the drain and both of my gray tanks were pushing the belly down when loaded. One is under the storage compartment and the other is behind the drop frame in the rear belly area.
I decided to support the three tanks with a product that can be purchased at Lowe's and Manard's. It is a wire shelf system called HyLoft. I used the 45"x 45" kit and cut it to size to fit under each tank. Each tank takes a kit and there are parts in the kits I did not use. J bolts or hand made hangers can be used to hang the supports from the angle iron tank frames. Be careful not to use something that might puncture the side of the tank. I made some hanger rods from 1/4" steel rod and threaded each end. The beauty of the wire shelf system is it will conform to the compound angles of the tank bottoms. I used 3/16" J bolts to fasten the center joints of the wire shelf to the supporting square tubing because the tubing needs to be above the shelf where the belly material is very close. The support is snug along the bottom edges of the tank but not tight enough to lift the tank. Also, it doesn't need to support the tank ends. There are about 6 to 9" unsupported on each end.
I have attached a few photos of one of the tanks with the support attached. Lastly, the storage floor has been removed for replacement because of water damage. I posted that in the general section as a problem with fungus. I will complete that thread in the near future.
I decided to support the three tanks with a product that can be purchased at Lowe's and Manard's. It is a wire shelf system called HyLoft. I used the 45"x 45" kit and cut it to size to fit under each tank. Each tank takes a kit and there are parts in the kits I did not use. J bolts or hand made hangers can be used to hang the supports from the angle iron tank frames. Be careful not to use something that might puncture the side of the tank. I made some hanger rods from 1/4" steel rod and threaded each end. The beauty of the wire shelf system is it will conform to the compound angles of the tank bottoms. I used 3/16" J bolts to fasten the center joints of the wire shelf to the supporting square tubing because the tubing needs to be above the shelf where the belly material is very close. The support is snug along the bottom edges of the tank but not tight enough to lift the tank. Also, it doesn't need to support the tank ends. There are about 6 to 9" unsupported on each end.
I have attached a few photos of one of the tanks with the support attached. Lastly, the storage floor has been removed for replacement because of water damage. I posted that in the general section as a problem with fungus. I will complete that thread in the near future.