I had one, back in the spring (I'll post back when I dig up the pic). Coming up through the pipes is the only way we could imagine it got there (unless I shit it out), as it was in the bathroom at the end of the house opposite the front door or garage, around the corner, and off the bedroom. I guess it could have creeped in somehow and made its way to a dark/damp area, but...
I was going to take a leak before bed and I didn't turn on the light (enough from the bedroom). I saw something dark in the bowl and thought someone hadn't flushed. I turn on the light and see this huge treefrog hiding on the inside of the bowl. After getting a camera, my wife, and mother-in-law (who was vacationing with us) and a bucket, I reached in to get him. He jumped onto the shower door, then onto my elbow, then into the bedroom (as my wife screamed and tried to close the door in time), then onto my endtable, then onto my elbow again. I stuck my bent arm into the bucket and rushed him outside through the front door. I like to think he stands guard out front, keeping away the home-invading FL insects, as thanks for
the rescue (bleach??? I hope your visited by a humanoid from the deep

).
In other Florida frog-related stories, my next door neighbor brought over a jar teeming with tadpoles for my daughter's 4th birthday in July (after I told my Mom, no fish/hamsters/etc for her grand-daughter). It's been a fun summer seeing them change into frogs and letting them go. We asked our neighbor what to feed them when they start to make the transition to legged lung-breathers and she told us she would bring over some mosquito larvae she could scoop out of her rain barrel. Well she she came over with another jar of the teeniest tadpoles and said "The adults will eat these little guys. Just tell your daughter they're going to visit the big ones." We couldn't bring ourselves to encourage cannibalism, so we raised about another 100 over the past couple months and let them loose. We only have a couple dozen left. It's strange as they don't all develop at the same speed if you have a large population. Some days we let go a 1/2 dozen, others one.
The treefrogs (like the lizards) live in the bushes outside our windows and come feed on the bugs at night who are attracted to the lights inside. Like living bug-zappers. They put on quite the show. When my daughter was about 2, she would sit on the window sill watching them catch bugs and say "Ricket, ricket, little fucky".
EDIT: Here it is...

The "Hopper in my hopper"... the "Croaker in my crapper"... the "Potty-wog"... Or for you Brit Chewers, a "Toad in the hole" (even if frogs and toads are different critters).