Is that one inch conduit ? If so, 3/4 inch fits rather nicely inside it. You could make them into rotary sleeve valves by having 3/4 conduit inside the 1 inch.
Drill matching holes from the 1 inch into the 3/4 inch. With the 1 inch tubes fastened in place so they don't move, when the 3/4 inch tubes are turned they will start to close off the 1/4 inch holes because of the holes going out of alignment. That will restrict all the holes in the pipes equal amount at the same time.
Edit, ok, I see your using 1-1/4 inch. How snug does the 1 inch fit inside it ?