I don't know why you find it hard to believe the frog came from the sewer. The sewers are full of critters. I have personally found big 'ole rats in...
The "illegal and dangerous" bit comes from the fact that your installation poses the risk of contamination of your (and the public's) drinking
water...
Pipe fittings generally require the use of TWO wrenches to install and remove. In your case, a large adjustable wrench on the valve, and similarly on...