My grandmother (house full ohn boys but only 3 girls) solved it this way:
Everyone has to sit.
There was some ignoring her in the beginning... And some retaliation. If she had to deal with other people's pee, they had to deal with hers. Just use your imagination. EVERYONE, by the way, so if even one person "cheated" they all suffered.
She also hung a 'testosterone' sign for guests/friends/etc;
If your hose is short, or your pressure is weak, better stand close or you'll pee on your feet.
In my house, I altered the rule a tad.
- Toilet seat left in the up position (I'm the only girl)
- toilet AND floor cleaned on a daily basis. By those who want to stand to pee. Doesn't matter if it LOOKS clean, it's cleaned every night before showers n stuff. ANYTHING OBVIOUS cleaned right there and then.
- no rugs to absorb pee (hide it) and stink of it
EVERY DAY... Or sitting. 2 options.
I hadnt cleaned the toilet in 7 years (until custody split, now i clean it once a week when kiddo is gone.). It's pristine.