I'm trying to pipe rainwater into my cistern under my house. I'm trying to find an overflow controle method. 4" auto valves are to expensive. Thought about putting a ring around in to raise the top up far enough to put an overflow pipe but I don't think I could get it to seal right. Is there a certain amount of pipe I could put down into the cistern to stop the flow naturally when it gets to a certain level? Sump pumps won't keep up with the amount of flow we get in bigger storms. My pipe is 4" connects to a filter bucket on the gutter. Runs under the house in the crawl. I plan on putting an overflow just above on my bucket to route extra water away. Any help would be great. Thanks.