Set the boots in a bucket or tub of water for 30 minutes. If there is a hole, it will not take long. Water always finds a way, as they say.
I disagree with pouring the water inside the boot as this is a good way to break down the interior padding, gluing, etc...
I know you sweat in them, but filling with water is just asking for problems. They are designed to keep water out, not hold it in. I am sure it will hold it, but just say... Now if they are all rubber boots, then fill'em up!
Just my $0.02