On most of my inverted glow engines I have the muffler below the engine head. When I fuel the plane excess fuel runs out the muffler. On a few I remove the pressure line while fueling. You can use different fittings or routing to help you eliminate the chance of hydro-locking the engine with excess fuel.

Also I always disconnect the fuel supply to the carb by using a fueling fitting that does this. You don't need anything complex or elaborate for this.

I like the World Model's fillers...



As far as setting up the plane, here is a tip.

Get the engine running upright, even if you have to flip the plane over initially. Leave the glow plug on and get the engine idling.
.
Turn the plane upright ( engine inverted ) then remove and re-install the glow plug igniter. Listen for ANY DECREASE in RPM's as you do this.
If RPM's decrease when you remove the glow lean the engine and try again.

Set the idle speed screws so that removing the igniter results in no change at all. You'll find that this will give you a reliable idle and the engine will not bog down over time.

Double check your high speed needle with a nose up down test, and have at it.