Mostly we use the freedom breeder tubs with a water bowl built in, no tipping. An easy fix would be to get the PVC couplings and cut them to where they are only about an inch or two from the top of the "roof". This way there is no room for tipping and the snake can only fit enough to have a drink.

As for not seeing the snake drink water.... Unless you spend 24/7 watching your snakes, the observation doesn't provide a reliable estimation of water consumption. Better to be safe than sorry.

However, it would be cool to conduct an experiment to see the amount of water consumed by a ball python. Maybe with a long term video? Even then there will be a significant difference I bet, depending on humidity, temp, age, individual snake, etc....