I just replaced a toilet in the second floor bath. I've noticed the water level drop in the bowl while watching it. Additionally, my wife flushed the 1st floor toilet and I watched the second floor toilet bowl water rise up and fall to just above the trap. Is this a vent problem or flapper not sealing correctly?

Hell Kpag,

The first thing I would suggest to check the small refill tube properly installed into the overflow pipe, see the image below, Thanks.

John

I am 99% sure your vent stack is clogged.

Thanks. I've heard the vent pipe could be the problem that allows water to drain out of the bowl. By the way, the refill tube is in the proper position. At least I don't have to take the toilet back.

I've heard that you can use a garden hose to wash out the vent pipe. I assume the water would drain into the sewer pipe. Is this correct?

A garden hose can be your first try, if it is safe to get on your roof.