On many RV’s and almost always on a 5th wheel there are usually two 45 Deg. turns in the pipe between the toilet and the tank. At the factory when the pipe is glued together a small lip forms on the bottom of each glued piece. The tool will almost always hang up on those lips when you try to smoothly force the pipe down the toilet through a plug. The easy way past them is to push the pipe in until it sticks on the lip, draw it back 3 inches and thrust it in with a fast sharp twisting thrust. It will jump past the lip and likely hang on the next one. If it does, just repeat the step at that level. A fully inserted tube will bend in the bottom and the water valve should be below the lip of the bowl. The main concern here is the valve in the toilet. It must be protected with a Johnny Chock or a similar pvc pipe that will do the same thing. (Be careful to not let the PVC pipe drop into the tank line). Just insert the Tank Dr. tube through the middle of the pipe that is holding the valve open. The ABS plastic pipe on the RV is MUCH stronger than the Pex pipe tool so it will not damage a properly installed tank or lines. It is possible to break the nipple off of the tool, but that will not effect its performance in any way. It is just a re-stricter to increase the velocity of the water. Now turn the water on and watch the water level in the bowl. if the water is rising, push the wand in further. If no water is rising in the bowl, very slowly draw the pipe back 3 inches with a twisting motion and let is set for 15 seconds. Repeat this process until the water in the bowl empties. There may be sludge in the pipe itself so even after the water clears the bowl, keep cleaning the pipe all the way to the top. You most likely have a pyramid plug in the tank that is blocking the toilet from emptying, but the tank itself is basically empty. After you have cleared the plug and cleaned the pipe and tank, close the valve outside and add 2 ounces of TankTechsRx to the tank and flush two full toilet bowls of water. Use the tank normally and treat according to the label instructions, especially the part that says do not empty completely. It would be advisable to rerun the pipe in the toilet in a couple of weeks as a precaution to blow out anything that may have been hardened and remains. It will now be soft and will wash away quickly. How fast you can clean the tank largely depends on what chemicals you have been using. In my experience, chemicals used for tank treatment will crystallize and increase the struvite level in the tank and take longer to clean. TankTechsRx will soften and eliminate them over time.