The only time I've ever drained them was to make a salsa when my fresh tomatoes weren't ripe enough.
Re rinsing the tin: I usually put a teaspoon of vegetable bouillon powder, tomato purée and any herbs I'm using in the tin, add a little boiling water & swirl, add to pan, then rinse with a little more boiling water (I learnt the hard way not to fill the tin with boiling water and then pick it up - obviously the tin gets very hot! )