I suggest to centrifuge the lavages through a 15 mL Centrifugal Filters (https://www.emdmillipore.com/US/en/life-science-research/protein-sample-preparation/protein-concentration/amicon-ultra-centrifugal-filters/15-ml/Q5ab.qB.pKIAAAFBuLplvyxp,nav) reducing volume to 1 ml before adding Trizol. For RNA extraction I would use 0.75 mL of TRIzol per 0.25 mL of your concentrated sample.