I know it's been months, and you've probably solved your issue, but I'll offer this up. If it's a threaded elbow, use a toothbrush to get it very clean, and use teflon tape. If that doesn't work, and you don't plan on unthreading it soon, try tub/tile caulk. It can be removed fairly easily for disassembly. If it's not a threaded connection, use the two-part pvc glue. It's for potable water systems, so safe. There's a purple primer, and a cement. I had to build a couple of parts to get my two systems to run end-to-end since I have a long skinny space, and was able to solve each of my leak issues with one of these approaches.