Some thoughts on the failure. Post baking may improve fusion. Or, because all of your filaments are circular/radial to the applied force, consider something as simple as a bonded wrap of paper (glue paper on the outside). You will be amazed how much gluing paper with epoxy to the outside of your silencer tube increases strength. Consider taking higher stress components, like air strippers, and make them press fit parts out of brass. Epoxy bind the brass parts to the 3d fabricated part. If you want an all plastic part, consider making the Outer diameter of your tube slightly smaller than the Inner diameter of a hot water PVC pipe, put epoxy on the outside of your tube, then slide the Hot Water PVC pipe over your finished tube before the epoxy cures. Hot water PVC pipe is more "chewy" than the more brittle white cold water PVC pipe.
The last part falls to the 3d design itself. If the wave generated by the first stripper stage (which is moving towards the exit end of the assembly), it met by a returning wave from the last stripper (which will be moving towards the entry of the tube), meet in the middle, they will make a high dynamic pressure stress zone, and cause failure in the middle of the assembly. The force of the colliding waves with be quite high. You mitigate this by having all reflection zones with a curved radius to diffuse the sharpness of the reflected wave. If you think of the impulse as a sonic wave, which you wish to scatter, it is more intuitive. Sharp corners on the interior are the enemy, and make problems both structurally and sonically. Or, you can just make it so strong, via the methods in the previous paragraph, so that good acoustical design does not matter.