<prompt> Most useful investigation for VVFThree swab testCystoscopyUrine cultureIVP  <response>: Big fistula Fistula tract is available Obvious escape of urine Tiny fistula Dye test Knee chest position: Escape of bubbles on coughing Three-swab test Gold Standard Cystoscopy Ref: D.C.DUTTA;S TEXTBOOK OF GYNAECOLOGY; 6th edition; Pg no: 420 