These two water toys are oil based toys.

In the first (bubble tube) air is allowed through the oil in uniform sized bubbles at regular intervals no matter what angle the toy is at. This is my favourite as it stays the same whatever happens around it.

The second (ooze tube) allows a stream of oil to flow into the lower half of the tube at varying rates depending on the air passing through the oil to the upper half.

(My apologies for the quality of the picture - having trouble getting the light ok)