I had a sink in a 1st floor bathroom that got clogged and overflowed for about an hour. I would guess about 10-20 gallons of water. Hard to say. Here's where it gets interesting.

There was a duct directly in front of the sink next to the vanity. The water did not pool, does not appear to have damaged any drywall or tile floor. Instead, it flowed down the sink, and directly, DIRECTLY into the ductwork. After some shopvac and towel work the bathroom LOOKS fine.

Now I go into the crawlspace. The duct was FULL of water. The ducts are RIGID ducts. They are drenched, inside and out. On instruction by my favorite HVAC guy, I cut the place in the duct where water pooled visibly and another 2-3 gallons poured out. The Crawl has like 3-4 gallons of pooled water in it, but I have a dehumidifier down there. I am not worried about Drying.

I AM worried about my subfloor (I have no insulation in the crawl and cannot see any visible damage), the wall behind the vanity (can't access it), vanity is against the wall but looks fine. But I am MOST worried about the ductwork. Full replace? Will it dry out? Should I submit a claim?