Im planning on joining a gym. Does anyone have any advice on how i can explain to a perspective personal trainer that im trans, living part time and don't want to bulk up but would want to slim down and build lean and tone muscle mass?

I don't think you would have ro tell them you're trans.  Just let them know what results you are looking for. 

Just stay away from weights and heavy paper body workouts. The weights can contribute to testosterone production and the heavy upper body workouts can increase your torso & shoulder size.

I have found that aerobic workouts tend to be best for slimming down and toning.

Thanks, cuz right now my goal weight is 160-170lbs and with not being on hormones i know its gonna be really easy to bulk up accidentally which in the end just means more work for the hormones to do.

You are most welcome Kariann. I think we most of start we struggle with weight and weight distribution.

Just stick to what ever you decide to do for diet and exercise. There will be days and weeks where it seems hopeless but if you stick with it you will get there.