Toto washlet hose extension kit
I'm posting this as general information for anyone who ran into the same problem I did regarding the installation of Toto's washlet and their Aquia toilet. The model of Aquia I own is no longer made, but this may apply to any of their toilets that have a skirt that obstructs access to the fill valve inlet.
Access to the fill valve inlet--let's say you're changing a fill valve--of some Toto toilets requires that the tank be removed and the water line be connected to the fill valve and threaded through a hole on the back of the toilet before the tank is replaced. In some cases, the water line is impossible to screw on to the fill valve if the tank is in place. This is a pain, but not a problem, if no washlet is involved.
The washlet uses an adapter that diverts water to the fill valve and the washlet. This is a large adapter that I believe comes with the washlet kit. If access to the fill valve inlet is unobstructed, then making these connections is easy. But if the toilet has an obstructive skirt, the connection between the water line, the washlet adapter, and the fill valve is very difficult to make. I got nowhere with calls to Toto consumer customer support.
My local plumbing supply called Toto and found that the fill valve requires an extension. The part name is TOTO 6" WASHLET HOSE EXTENSION KIT. The part number is THU9090R.
I hope this makes installation easier for some folks.