Well. Trichomoniasis cannot be spread through toilet seats. Just think, if it does spread every tourist will be affected. So, what you have heard was wrong.
And, I am 100% sure, that trichomoniasis spread only through sexual contact.
It's possible to get trich from a hot tub, if the hot tub isn't cleaned, and maybe a toilet seat (there is some debate about that, and I'm not sure I believe it, or we'd all have it).
Is there a reason you are asking?