The EPI 4580 waste tank is manufactured with a 3-inch discharge outlet, making it fully compatible for use as a black tank for RV toilets. Although product images may show a 1 1/2-inch reducer attached, this reducer can be removed. It is secured with a butyl seal and compression fitting rather than glue. To remove the reducer, loosen the compression clamp and apply moderate heat using a heat gun or hairdryer to soften the seal, then carefully slide off the reducer. If preferred, a replacement 3-inch outlet part can be sent to you at no cost with expedited shipping. Alternatively, you may return the tank if it does not meet your needs. Our goal is to ensure you have the correct part and a hassle-free experience.