Fuel flow issues in 1.2

[magnemoe]

This is stupid.
Rocket is mostly empty tanks so I thought I could use the tanks as part of first stage.
Central tank, radial tanks for second stage engines, top drop stage and first stage, small SRB for twr at launch. 


My plan was simple let first stage use the upper drop stage, central tank and the 2.5 and 3.75m first stage tanks, second stage uses the 2.5 meter radial tanks who is not topped to finish gravity turn and circulate, then dock with fuel depot for more fuel for going to Minmus. 
Purpose of craft is to transport gold from an Minmus mining base to Kerbin, its heavy so I need the overpowered engines, drop tank is for Minmus accent and the return burn, its dropped before aerobrake. 

My problem is that the first stage will also drain the radial second stage tanks. Is it an way to avoid this? I have fuel lines from center tank to the radial tanks. 

[magnemoe]

Solved the issue using an bypass pipe.

I might not need to eject it 

[Red Iron Crown]

You could also work around the issue by manually lowering the priority of the radial second stage tanks. The first stage would still be able to drain them but would drain the other tanks first.

[Clipperride]

The tweakables allow you to order the way tanks drain, going from the highest to lowest numbers. What has thrown me several times is, you need to enable propellant flow across all the decouplers, separators and docking ports.  Otherwise each stage acts as a separate system (which can also be useful)

[magnemoe]

5 hours ago, Clipperride said:

The tweakables allow you to order the way tanks drain, going from the highest to lowest numbers. What has thrown me several times is, you need to enable propellant flow across all the decouplers, separators and docking ports.  Otherwise each stage acts as a separate system (which can also be useful)

I know, I could set it up so, first drain the first stage tanks, then the long 1.25, then the orange one and last the 720 liter ones. however I then had to watch the fuel level of tanks inside an fairing, kill trust then the orange tank was empty, stage and continue with upper stage. 
However using the bypass I can let mechjeb handle the launch and this is an standard payload.