This is a good guide for a proper clean out of the Grobo.
When you harvest, I would suggest draining the unit completely, getting all the water out, and giving it a good wipedown with some vinegar and then possibly isopropyl after before drying. You could end up doing the full clean out, but typically I would suggest getting your plant trimmed (if you choose to do so) and hung as soon as possible to start the dry and cure pretty quickly.
It is a good idea to hang your pH probe in a plastic baggie with either distilled/RO water or a storage solution to keep it saturated while the dry process goes on/ inbetween grows. You can use magnet hooks to hold it in place while it sits in the liquid.