Basically, You get a silicone mask that you can replace the filters on.
Use the filter pores and locking system to connect the valve and the pipes.
(The valve can be constructed using a syringe and a ball.)
Connect a 20 mm pip to the valve, and a larger cylinder (syringe) to the other end.
Place a HEPA or N95 filter in the cylinder.
You can wear this under your clothes behind you (on you back side).

The parts are all washable, but the filters can be discarded or if reusable, washed and made ready

My idea is that because the filters are under clothes, it is better protected from being exposed to virus loads (coughing, droplets). And we can use less filter material for the filter over a small cylinder.