Just let piss go. On the skin, in the clothes, in the mouth…
HIV and Other Infections
You cannot contract HIV through piss—even if someone has an untreated HIV infection. This is true even if there are small amounts of blood in the piss: The urine dilutes the blood so much that HIV transmission is not possible.
Hepatitis C is also not transmitted through piss. However, if there is blood in the piss and it comes into contact with mucous membranes or open wounds, hepatitis C can theoretically be transmitted. The same applies to hepatitis B.
You can get vaccinated against hepatitis A and B. There is no vaccine for hepatitis C, but the infection is generally easy to treat and can be cured.
Test
Get tested regularly for HIV, hepatitis C, and other sexually transmitted infections (STIs). How often depends on your sexual practices and your individual risk. Swabs from the penis, anus, vagina, front hole, neo-vagina, and throat may be helpful because infections in these areas often cause no symptoms. Vaccines are available for hepatitis A and B. Here you can find testing sites near you.