Does peeing before intercourse eliminate sperm in pre-ejaculate?

It would cut it down. It's NOT a good birth control method. It's merely a reduction in the probability of conception. If there was any recent flow of sperm (masturbation, etc) most will wash away w/ urine, but no guarantee for all. If you've missed a period, do a test and in the future use real protection. For pregnancy AND STDs. It's smart and caring. And that's sexy.
Unfortunately not. Washes any sperm lingering in urethra, but does not wash out Cowper's gland duct where some sperm now be hiding, waiting for release of pre-cum from Cowper's gland & why coitus interruptus is an unsafe form of contraception.
Not likely. No. Urine is acidic so it might have a minor effect on the sperm.