Hi Guys,
With purp venosa as one of the parents, I fill the venosas with water to help them catch. With mitcheliana type hybrids, in practice I don't fill them up at all, but unlike the trumpet type pitchers such as flava etc, and depending on the strength of the pitcher, it may be beneficial to it to have a little bit of water if you are gowing indoors. This type of hybrid is not a very successful insect catcher for me, and some of the plants don't get anything all year. But they still grow OK without!