Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4566351.
Note: This design requires the use of flexible material for the 'insert' and 'gasket'. Optionally use a rubber gasket (garden hose gasket works well) or actual 3M mask washer for the gasket.
This adapter provides an attachment point to add a filter to the exhaust valve of a 3M 6500 series half mask. Normally, exhaled air is simply exhausted directly to the surroundings via a one way valve. This is perfectly acceptable when using the mask to protect oneself from the surroundings, however it does not necessarily protect the surroundings from the user.
This adapter fits into the exhaust slot in the mask and provides a 3M bayonet attachment point for a filter. You can use any of the designs that fit to the standard 3M port, but I recommend something on the smaller side. I use my mini filter (https://www.thingiverse.com/thing:4219678), but there are plenty out there.
If your filter material has a preferred flow direction, keep than in mind when constructing your filter, as the airflow through this is the opposite direction of a normal filter use scenario.
Note that this does interfere with the use of the "Quick Latch" feature found on some 6500 series masks.