0600 hours this morning the wife gets out of bed to use the master
bath (on second floor). She screams because there is a small gray
mouse doing the breast stroke in the toilet, stuck unable to climb
out. I figure since this is a second story bath that the only way
that mouse got there was through the roof vent. We've never had a
mouse in the house and it would be impossible for him to get into the
toilet by climbing it or jumping from a counter because this toilet is
separated from the sink in a corner with no adjacent fixtures. I also
figue it could not have crawled up to the second story through
vertical PVC from the basement had it gotten in through the street
main.

So it must have fell in the roof vent then just too a turn at the T
into the toilet and swam past the toilet P trap.

Is there any other way he could have gotten there? That I should be
looking to plug up an entry hole? The house is only 8 years old,
probably no screen on the roof vent.