I’ve used this page (https://genesis.farm.bot/docs/capture-and-use-rainwater) for inspiration on rainwater.
Once at step 4 it suggests to replace the valve with the pump (unless your rain barrel is significantly higher in elevation than your FarmBot).
I have both on the same level, just the rain barrel is higher (1.5m) then the FarmBot. When the rain barrel is (near) full, the water level is a little higher, which gives a little water pressure. Due to communicating vessels, the water keeps flowing. Therefore I would suggest to install a pump but don’t remove the valve.
Maybe useful enough for adjusting the https://genesis.farm.bot/docs/capture-and-use-rainwater page.