I built the sink vanity. I used the original height of the vanity and measured an appropriate distance from the toilet to make the space feel comfortable. The countertop behind the toilet is mounted on a hinge so you can lift it up so you can store things.
I used this pool and spa vacuum hose to replace the filler tube to the water tank. I found out later you can get original filler tube from a trailer supply store. Oh well, it worked.