So I'm still fighting with this water leak. I shut down all the water sources and let everything dry up then started to rule out a few things. I turned on the water pump for a few days, no leak, took a shower and let the water run no leak. The tank was starting to get low so I filled it. I didn't check for a leak right after filling it but the next day the leak was back? Is it possible the tank fill somehow runs under the shower? I did notice under the bathroom sink some kind of what seemed like a vacuum breaker? Is that part of the tank fill? I wish I could see things better but no access. The pipes only run under there for a short distance.