Tight enough that it holds it down but does not snap the leads off.
Edit: oh the rda, snug not tight.
Gotcha.
So, we have Multipul tanks? on Multipul Mods? with Multipul Builds? and nothing is working?
Did you clean everything at the same time? Is it possible you contaminated everything?
*Note - No Air Flow when firing should always cause the Center to Rapidly Dry First.
Air Flow helps disburse Heat. If it still over heats with Air flow, Turn it down. If it still overheats, Question what is going on with the Mod and turn it down further.
Wattage Delivered should only be as high as needed to Smoothly Vaporize the e-liquid. Whether it be 8 watts or 150 watts - Build dependent.