I have learned along the way that the back flow of air through the pump IS definitely a problem, especially when working with air tight systems or relatively low height water columns. For this reason, I have added two mechanism to aid with the control of the fill and drain cycles. I have also added a central "manifold" through which all air flows, allowing for expansion/experimentation.
The air escaping through the planters, when the reservoir empties, was also a problem, so I added a separate bottle that I call a bubbler. The bubbler redirects the escaping air and reduces the bubble size, reducing splashing, vibrations and effectively extending the pump on time. I suppose it could be used as a planter as well. Don't know what you'd call the bubble method.
The MODULARITY has been expanded so that the "HUB" of the system is the Bubbler and the TEE below. Everything else is swappable. You can change reservoirs and/or reservoir types as well as "planter lines" and types of planters at your whim. This allows for experimentation and expansion without having to disturb that which does need to be disturbed.
I do plan on improving/screwing with stuff as time goes on and required a "productive" window sill garden that accommodates different designs and methods, without starting from scratch each time. This what I've come up with and hope to be adding "Modules" as time goes on.
Step 1: Modular Reservoir
1 ea 2L pop bottle with cap
Approx. 18 inch length of 3/8 inch OD Vinyl tubing (trim as required in final setup)
1 ea 7/8 inch length of 7/16 inch OD tubing
1 ea 5/8 inch length of 1/2 inch CPVC tubing
Hot melt glue (Silicone would probably be best)
WHAT I DID
1. Drill one each 5/16 inch and 13/64 inch holes in the cap as shown.
2. Cut both ends of the 2 ft length of tube on an angle as shown.
3. Thread the 2 ft length of tube through the 5/16 inch hole in the cap as shown.
4. On the end of the same tube, that will be outside of the bottle (cap orientation), slip the 7/16 and 1/2 inch pieces over each other as shown to form an adapter.
5. This adapter will leak without tension applied, so hot melt glue as shown to seal.
5.Place cap on bottle and adjust tube so it reaches the bottom of the inside of the bottle.