Any thoughts on tube size for the fill/drain line?
I'm thinking of using 1" PVC as that's the largest size I can get a Solenoid valve for pretty cheeply. Here is an example
1" Electric Solenoid Valve 12 volt DC VITON SEAL B21V | eBay
I'm not too concerened with how quickly it drains, but I don't want it to take an hour to fill either. I'm just think of how long it takes for my sink to drain and it's just a few gallons. I'm guessing 30 gallons through a 1" tube is going to take a LONG time.
Filling should just be a product of the pressure I use on the regulator. A bit more pressure should increase the flow rate.