My version of the milk jug fly trap to fit in the opening of the jug with a snug fit.

Model Edit: 

V1.1 - I made a slight change to .stl to mate the sleeve to the trap top for better build adhesion.   If you downloaded V1.0, superglue the sleeve to the top portion and you should be good to go.
 

Neck measures 28.20mm for a snug fit.

Print with light supports, set supports at 65 degrees.

• You can see printed traps with and after supports removed.

I like to print Dynamic 1.6 for a cleaner print look

Printed with Elegoo PLA+

• Green printed using Ender 3 V1.0, 
• Blue printed on Qidi X-one2.  

Add a vinegar to water in a 1 gallon jug and hang from a rope.