If someone has an STD and you sit in that persons pee for awhile then yes you could likely get an STD from sitting in the persons pee.
However if you just accidentally sat in someone else's pee for a second then cleaned up right away then nothing bad is likely to happen.
However sitting in pee including your own can lead to Urinary Tract Infections and a rash.
Just like a baby or toddler or even an adult who is wearing diapers and the diaper does not get changed often enough.
The baby, toddler, child or adult could get a Urinary Tract Infection from sitting in the pee diaper too long.
This is especially true with girls who sit in a wet diaper because the pee that goes stale and grows bacteria can get into the vagina.
So that's why diapers when wet needs changed often enough within about 3 hours.
There is a small chance that you can catch an STD from bathing with someone who has it.
If someone who has an STD bathes with someone who doesn't then the STD could come out of the infected persons body and then enter the other persons body.
But it's rare to get an STD from simply bathing with someone.
That would also mean that you could get STDs from swimming in a public swimming pool with people or someone who has it.
You're more likely to get an STD when having sex than when bathing but it's possible.
Also you can sleep with someone who has an STD and not get the STD.
Simply sleeping with a person who has an STD won't cause you to get the STD yourself.
To get the STD you need to have sex with the person who has the STD or lick a persons Vagina and then you contract the STD.
But it's safe to just sleep with the person who is infected with an STD.
STDs can live on surfaces but only for a short amount of time.
STDs have the ability to live on the outside of the body for around 1 hour or less but any longer than 1 hour the STDs would have a hard time surviving.
That's why it's basically impossible to get STDs from toilet seats, towels etc.
But it's still good to disinfect surfaces such as toilet seats and also use a toilet seat cover on public toilet seats because you could get other infections that may live on the surfaces.
I always bring disinfecting wipes with me to public restrooms and wipe the toilet seat down before sitting on it and I also add some toilet paper to the toilet seat.
For an STD to live though it needs to be in the membrane to survive longer.