Hellooooo,
I tried the inline route (20 micron sock on the hydromaster filter in the hydromaster filter casing - filtering while still in vacuum. It does work but it also gets clogged quite quickly and if you've not used a hydromaster filter before ..... d**n they're bulky if you're out 'n about with your porty)
If you find that the Ninja waste tank is too small then try this .....
I've padded out the lid of the clean tank and put a catch on either side. Then install some waste fittings from your local plumbers merchants (with sealing caps) and connect the two tanks to make them one.
Why the sealing caps? If you like you can switch from recycling to clean tank / waste tank

Utter genius even if I say so myself.

'Corse if you stick with just the one recycling tank then you've got tool/ cable and packed lunch storage in the now defunct clean tank

The padded clean tank lid with catches is a must because not only is the solution split between the two tanks, the vacuum is now also.
Best
Alan