The rapid adoption of geotextiles in civil engineering stems from their exceptional drainage and filtration capabilities. Concurrently, the dwindling of natural river sand, valued for its superior permeability, necessitates sustainable alternatives. The present study evaluates the potential of fly ash-based (FAB) sand, as a novel alternate geomaterial to river sand for the drainage and filtration applications. Three variants of geotextiles (150, 200, and 250 GSM), polypropylene needle-punched nonwoven type, are selected for the study purpose. Four different gradations of FAB sand, such as coarse, medium, fine, and overall sand, are used to assess the drainage and filtration properties using a custom-designed gradient ratio test rig at hydraulic gradient of 2.2. The results reveal a distinct hydraulic behavior of sand-geotextile system. Gradient ratio test results indicate that coarse and medium sand exhibited identical trends across all geotextile variants, with 250 GSM showing a higher gradient ratio than 150 GSM. Whereas, fine and overall sand exhibited a higher gradient ratio with 150 GSM and the lowest with 250 GSM. Furthermore, permeability results reinforced these findings, revealing lower permeability for 250 GSM in coarse and medium sands. Notably, fine sand with 150 GSM had lower permeability than 200 GSM but higher than 250 GSM. These findings emphasize the influence of FAB sand gradation and geotextile mass on the hydraulic performance of sand-geotextile system for an effective filtration and drainage in geotechnical applications.