I installed it yesterday and I even got it right side up, but how tight is tight?

I used the stock fiber washer that it came with .. turned with an adjustable crescent with my hand holding the wrench and valve to reduce leverageand tightened until i couldn't reasonably turn it easily AND then turned it about a 1/4 way more.

enough, too much or or too loose?

 

Sounds fine to me; I have had a Fumoto on mine for about 3 years, without problems.

 

Sounds good, I have one on every car with no issues