Q&A for How to Detect Toilet Leaks

Yes, it will leak because the wax ring is what holds the pressure on the toilet. It helps the toilet flush, so if the wax seal is bad, the toilet will seep water out into the sewer. You can tell if the seal is bad by using a wax pencil to mark your water line at night when you go to bed. In the morning, if the water is below the mark, you need to replace your wax seal.

The fill valve is not shutting off when the tank gets full of water. Look in the tank to see if water is coming up over the overflow tube. The water level should be just a little lower than that.

Replacing the "flapper" will usually work. Replacements can be found at Home Depot, Lowe's, Walmart, etc.

Where is it leaking, into the bowl or externally? There is a wax washer usually between the bowl and the tank. If the toilet is old, I would consider getting a replacement.

A leak in the toilet drain, and I'd get this one fixed, it could cause a lot of internal damage.

Maybe. If the bathroom is humid, and the toilet is flushed fairly often, and the water supply is cold, then condensation can occur on the outside of the tank, perhaps with dripping, even if the toilet is not leaking. If the toilet is leaking (for example, water level in the tank is high enough to cause water to continuously drain through the overflow tube), then the water in the tank will always be cold (depending on the temperature of your water source) and condensation is more likely.