As far as I'm aware they all need draining. I've worked on an eMac and iMac g3 and those the crt retain charge.
Easy way to be sure - when you turn it off and turn it back on, does the picture come straight back or does it slowly fade into existence as if you were turning it on with a dimmer switch? If it fades in the tube had been discharged and the picture did not return until the charge had built back up. To be safe discharge before use from under the sucker cup, discharge large capacitors and then make sure you are earthed through a wrist strap - it's good to get in the habit of taking as much care as possible. And again it's critical that you are not earthed before discharging. See my previous post.