If you can reach up in the back, follow the pipe till you get to a somewhat knurled nut/fitting on the pipe. Grab it with your hand and try to tighten it. If the leak continues, you'll need to unscrew that nut, pull the pipe down so you can get to the end of the pipe. Inside the nut, there will be a rubber seal. Remove it with a pick and go get some cone shaped seals from a RV store. It won't look at all like the one you removed because yours will be flat from being compressed. Put the new seal inside the nut and make it back up hand tight.