User chapsley asks: I poured five gallons of water directly down the drain and didn't get any leaks, so I believe it's the tile. I've ran silicone caulking around where the floor meets the wall and the leak has gotten better but not gone. Anyone have an idea how I should proceed?
Answer: Tear it out. Install a shower pan and re-tile it. It sucks but that's your only real fix.
ItJustGotRielle adds: Unfortunately this is the case. The pan and membrane were not installed or were installed incorrectly.