I can understanding not wanting containers in the tub. My daughter loves to drink the bathwater, too. :)
We have the Boon foam toys that stick to the walls of the tub and any other flat surface (including tummies and foreheads, briefly). They stand up well to biting. My daughter has put tooth marks on a few, but hasn't actually bitten through any of them yet.
Another one we have is a whale shape sorter with four shapes by Alex company. The pieces could be used for drinking, but my daughter likes to play with it. My only real complaint is that the tabs that hold the bottom of the whale to the top broke easily. But the set still works using just the top.
One grandma has a set of rubber ducks that float, light up and quack a song. They're sealed so they don't end up with water inside. She also has a small mesh basketball hoop that suction cups to the side of the tub with a couple of sealed plastic balls.
Another grandma has a set of hard plastic floating fish and a small net to catch them in and go fishing. That would probably be more appropriate for the older one.
I don't know the brands for any of the grandma's house toys, but I'm sure you could find something similar if you search. Good luck.