The filter unit is made of common household items. A tall plastic cup houses a finer wire mesh sieve and washing sponge form the filter.
Transferring the bird nest from the ultrasonic cleaner into the wire mesh sieve, it is then wash continually by circulating water. The finer wire sieve retains bird nest that overflowed into the filter cup.
I am pretty satisfied with the result. These are fine particles trapped by the filter sponge after cleaning - ones that can't be picked by tweezers.
So I am using a 2 stage process now. First using the ultrasonic cleaner (& hand picked the larger feathers of course) before transferring to the 2nd rinsing/filtration process.
A logical next step is to combine the two into a single process. But I am happy with this arrangement for the meantime. Hope you will find it useful too.