Is it possible to add liquid to wave machine?

[Tanya]

I recently came into an Adriatic Model 16 Wave Machine. It seems to be missing some liquid, enough to throw off the weight for proper operation. Is it possible to add liquid to one of these? And what would be the right stuff to add? Has anyone done it before? Thanks.

[Michael Nestor]

When you posted this it was just discontinued

[Jonas Clark-Elliott]

AFAIK, no, it isn't. The plug you see was glued in, I think using acrylic glue. If that's correct, the glue temporarily liquefies the plastic; when it solidifies, both pieces are now really one piece.