The answer by Shadow Wizard Chasing Starsanswer by Shadow Wizard Chasing Stars mentions incontinence briefs (there are also pads). These are a bit expensive and bulky, designed to hold much more fluid. For this purpose, a thin disposable "panty liner" will perform the same function. You will find them in the "women's" section of the pharmacy. They are a thin, very absorbent pad with a waterproof backing and adhesive to keep it positioned in your underwear. The thinnest ones are designed to hold at least that much fluid. This will protect both your trousers and underwear.