There is no room for what you describe. You cannot run a 3 inch pipe horizontally from the Pass side to the drivers side. We sold and serviced National from 1993 until they went out of business. What you probably have is a Down pipe that makes 2 -15 degree bends to go in the top of the tank. OR, you have a POOP pyramid where the down pipe goes into the top of the black tank that is restricting the debris flowing into the tank. I assume you are not the original owner. I would fill the tank as best as possible with hot/warm water. add triple the chemical and let sit for a few days or a week to help dissolve any debris in the tank. I would then drain about 5 to 10 gallons and observe the color of the debris coming out. That will tell you if there are abnormal solids you have dissolved. I would then get ready to test drive. Dump 4 or 5 bags of store bought Ice into the tank thru the toilet and then drive 10 or 20 miles making lots or turns and stops. The ice, before it melts will break loose any solids in the tank. Then dump and flush the tank 3 or 4 times and observe the color of the water coming out. If this procedure is done, the water coming out should be almost clear, That lets you know the tank is clean and no poop pyramids still exist. Then go on your next camping trip and see how it goes. Doug
