Seromas are an absolute pain in the butt and potentially dangerous! My personal best was one and a half litres in one aspiration, no exaggeration! Up to that point I thought a mastectomy looked like that, nicely rounded! My pet hate was when I bent over and audibly sloshed. Relatively painless as you say, problem is a nice little (or big) warm internal pond is heaven for the bad bacteria we all have. 2 infections were relatively mild but the last ( a year after surgery!) landed me in hospital for a week and heavy duty 24 hour antibiotics. Enhanced appreciation about the old line on death certificates of 'death by sepsis'! My surgeon did the right but slightly risky think of opening up my mastectomy scar and giving me a 'good scrub out'. A week of intravenous killer fluid hadn't actually touched the infection core, even though I felt a lot better, but the scrub out did. Goodbye seroma, goodbye infections, hello prosthesis (finally!). Don't let your gruesome little friend hang around is my advice, even though your body is trying to help. The intentions are good, but the outcome may not be and you have other priorities right now. Best wishes!