Did you suffer for years with RV toilet not holding water? Not to worry. BougeRV rubber flush ball seal is easy to replace and it keeps the water in place and the stink out..Easy installation, only been in place a few minutes. Just popped the old seal out (no disassembly required of the toilet) and put the new flush ball seal in place ensuring it's seated in fully..Our flush ball gaskets are a perfect fit for Dometic 300/ 310 RV, motorhome and trailer toilets. These flush ball seals replace Dometic flush ball seal kits # 385311658. DOES NOT FIT MODELS: 210, 510 or Other Models Not Mentioned..Outer Diameter: 4 Inch; Inner Diameter: 2.75 Inch. BougeRV flush ball seal is soft, firm enough to seal properly. Notice: Any use of a Dometic Brand or model name is used solely to describe & illustrate the compatibility of our product..What you'll get: 1 YEAR WARRANTY & Lifetime customer service. If you have any concerns or questions, please get in contact with BougeRV customer service.