I have been reading and talking in the harsh environment section discussing blowing out the tubing to prevent freeze.
I also wanted to see another tank added so that liquid fertilizer like compost tea could be added at will and I realize that the changes could be met with one change to the system.
And it would be a change that added more flexibility for other needs.
I kept coming back to thinking that there needed to be a change to the tubing system that normally is used for water. Now I think I have it totally imagined. I think there should be a tank before the tubing reaches the gantry arm. The tank (someone that understands me please give me name for this type of tank, overflow?) would have three or more sections of tubing that are incorporated into its cap and the reservoir part would screw into the cap, the cap being mounted part. The tubing coming into the tank from the outside would be controlled from switching valve so that you could choose what is added the other tubing leading to the gantry arm would just lead straight to the watering arm.
When you wanted to run a cleaning cycle you would keep you vinegar or whatever in the reservoir.
If you wanted to use a powered or concentrated fertilizer it would go into the reservoir and be mixed with water on the way out.
If you wanted to blow out the system for cold weather storage you would attach the second input tubing to your pressurized air source.
If you had a large tank somewhere that you wanted to dip into and suck up liquid to be used over and over again then you would be sucking it into the reservoir and then you could either let it mix with water and come out, be blow out with pressure if the tank is before the pump it could be sucked out.
I think this change would provide a lot of various functionality that people could get creative with.