You can level a tank to 20 or something also to just learn a little about them and give your tanks advice (but I would be careful on giving more advice than your tank experience). If the tank takes the advice, then it will help them and you.

For instance, I was in tam-tara with a gladiator that couldn't hold hate on multiple mobs after a couple heals. I suggested he fast blade, savage blade, flash, repeat. It's not the best advice because there are more things a tank should be doing but the advice was very simple to execute. The gladiator started doing the suggested rotation and we had much less enmity problems.