Milk Jug Watering Bulb

Got tired of having to take plastic bottles down to recycling
Got tired of having to remember to water my thirsty plants

The hole guide is set to center a 13mm hole for the stake in the cap. Drill hole slightly smaller if you want a tighter fit.
The stake slides in from the inner part and uses friction against the hole to hold in place along with the weight from water. Can also add some glue if you feel its necessary.

Have used this design with a 1.9L juice bottle and a 500mL milk bottle and fits both without issues.