of all sizes are offered for greywater & blackwater tanks. Our non sloped rectangular rv holding tanks are available with standard fitting packages with some tanks having a customizable “build a tank” option available. Our sloped rv holding tanks come with a premolded outlet and you can customize any inlets or vents on these tanks as well. Listed below are rv holding tanks from Todd, Trionic & Ronco Plastics great for any rv, camper, motorhome, travel trailer or food truck conversion.