I've read that you can't drown them, though you may get them to move out.
But, a home remedy I found is to sprinkle borax or soap flakes around their
mounds and water. The soap destroys their waterproofedness and then they DO
drown.

MDM wrote:
thanks for all the replies so far.
I do not want to use anything scary or toxic chemicals, I'm no old
hippie but I don't like dumping that stuff in the ground.
The drowning idea did cross my mind so I may try that. We do have a
vacant yard next door so the evacuation plan might work too.