Here's what was supposed to be the initial concept for a plant automation system. A pump / control head is mounted to a reservoir with 1.5 .. 20 L volume. The head contains a small brushed motor peristaltic pump in a pipe clamp with vibration damping.

The enclosure is made of DN75 pipe couplers and end caps which are easily available. A few 3D printed parts hold electronics and battery and connect to the reservoir vessel.

It turns out that there's a plethora of different neck finishes for PET bottles. Less so with canisters where neck finishes like 48/41, DIN45, DIN51, DIN61, ..are commonly encountered, at least for the 3+ L ones. The smaller PET bottles often come with PCO-1881 but then again there are lots of different other finishes out there with deviating pitch and numbers of starts (3-start threads are nice). We designed adapters for a selection of neck finishes, among them 38/33, 48/18 (5L spring water), Bericap 3419 (1L Granini bottle), Bericap 3439 (3 .. 5 L spring water), PCO-1881 (0.75 .. 2L soda bottles)

You do want to see the Granini bottle thingy, don't you?

To attach the pump head to a vessel, a few 3D printed parts according to the neck finish definitions are needed.

The cool thing about 48/41 is that it's a 3-start thread with a large pitch, so twisting the swivel nut by 90-120° undoes the connection and allows easy removal of the pump head for refilling.

We had a little bit of a discussion regarding funnels and how to refill the reservoirs. In my opinion the 48/41 adapter in conjunction with exchangable 5 L bottles is a great trade-off since it starts making sense to just swap the bottle for refilling.

There is a suction line running down the center of the adapter which needs a little weight at the end but that's about all to get the water out since the peristaltic pump is self-priming. One of the main features of the adapter geometry is that when tipped over there's hardly any spilling and leakage.

A detailled explanation on how to create the threads is given here:

https://hackaday.io/page/5252-generating-nice-threads-in-openscad

The design files can be found on github:

https://github.com/MisterHW/IoP-satellite/tree/master/OpenSCAD%20bottle%20threads

First contact with Reality

We never fully deployed the concept despite a couple of parts that were built and iterated to clean up minor defects since we realized that stuffing the electronics in the head would be fine for a single plant one would like to leave out in the wild, but not so much for a more diverse growing setup where one or two reservoirs are to serve 20-30 plants. Additionally the bulky head stops making sense below 3 L now that the electronics is stripped as well. It may have its place, especially when implemented as a cheap spare reservoir that connects to intermediate tubing before routing out to the plants. This would be ideal for setups that have to be readied for longer vacations.