Fluid or ascites may form in the open abdomen from liver involvement of salpingitis and other reproductive conditions and cancer. Here is some reading about salpingitis and caseous exudate (pus:)
https://extension.psu.edu/salpingitis-salpingoperitonitis
Many people use amoxicillin 250 mg twice a day for 10 days for salpingitis/lash egg, while others use enrofloxacin 10% liquid 0.25 ml orally twice a day for 5 days. Those dosages are for a 5 pound average chicken. Here is where to find those...