Three-way valve

This is probably fairly unnecessary, but a fun project. Run three softish silicon hoses through this and it will clamp two out of three of them at any time, using the servo to choose which one is open. This way you only need one pump for three pots. The construction is self-locking without screws, although you may want to use screws to fasten the servo. I used a "standard" servo, equivalent to a Futaba S3003.
I printed this with cheap ABS.
A very simple hose clamp for the edge of a pot is included as well, as a separate part.