Currently, there is no exact direct replacement for the Elk Plastics 230h holding tank with dimensions 12" high x 12" wide x 35–40" long in our inventory. However, we do offer a similar tank measuring 40" long x 14" wide x 11" high (Elkhart Plastics 19 Gallon RV Holding Tank - model 0189H) that might work if you can accommodate slight dimensional differences. We specialize in sourcing hard-to-find and discontinued RV tanks, so if you can provide additional details about the fittings—including their placement, size, and number of holes—or photos of your current tank, we can assist in finding the best compatible. Please contact us with this information to explore your options.