How long can sperm survive in the toilet bowl /toilet water? Chance of pregnancy from toilet splash when taking a piss/poop or from flush?

Not an issue. This is a non-issue, because nobody gets pregnant this way. No worries. If overly worried (which should not be the case for such non-issues) and not in a drought state like California, one can flush once and then sit down after the potential upward splash has subsided.