Water strainer installation

My boat does not have a water strainer, but considering the amount of debris that came out of the trans oil cooler when it was last inspected, I want to install a water strainer. Two questions:

1. I've read on some forum posts here and elsewhere that the strainer has to be installed above the water line. Why?

2. Is it important where a flushing connection (like a 'Timmy T') is installed relative to the strainer - i.e. before or after?

Thanks a lot for the help!

TRBenj wrote: If you want to empty the bowl while in the water, it would be ideal to not have water pouring in while doing so. Tee location relative to strainer doesn’t matter, but try to put it at the highest point to help the pump prime when the system is dry.