Update : sorry I noticed that the M10 thread accidentally was set for M11, I corrected this and reported it as v3 below for all the files. No other changes other then correcting the thread.

I built this adapter to allow me to switch from MMU to just using Single Filament by unplugging the MMU2 and unscrewing the Festo M5 push-in fitting from the MMU and screwing it into the adapter. The Adapter has a M5 threaded nut, you can buy this from Amazon in various packages, I purchased the selection, I also included the heat set insert you can attach to your soldering iron to press it in.

https://www.amazon.com/dp/B08YYGRCBG?ref_=cm_sw_r_cp_ud_dp_0WGR9XBZJ0V6H67E0KDC

https://www.amazon.com/dp/B09VL41T7K?ref_=cm_sw_r_cp_ud_dp_DVHRH3HRDC92SJF9VKWF

https://www.amazon.com/dp/B07P2XRCC1?ref_=cm_sw_r_cp_ud_dp_QWJQM50X8CGZMKQEFG2V

The adapter was printed with hole to fit the press insert, and threaded on the other end for a M10 PTFE Tube quick fit. I used this method because I can then push the PTFE tube through the M10 and butt it up against the Festo M5 to create minimal snagging.

I run a PTFE tube from the M10 up to the top of the Lack table where I can then feed any filament to it and manually load the filament like a standard MK3 once I power off the MMU. 

I don't like removing the PTFE tube on/off the Festo M5 connector because I find it bends the tube and I want to put minimal distortion to the tube.

I originally thought of just putting a thread for the M5 to the adapter but given amount of times I may screw/unscrew this I though it would be better to use a brass fitting and keep it clean. 

I disabled auto filament load feature and select load and material.

Print it on side no support needed.

I printed using PETG since it will be inside my lack case.