Hello there folks. I'm playing an Only War Campaign with some Deathwatch monsters and enemies.

Currently the players are fighting some Tau Drones (MotX) with a Firewarrior (Corebook). The Tau is wounded and one of the drones has an Injector with Pain Suppressants.

However the corebook does not say what roll or what kind of action is required to administer the PS. What do you think it is?
If no luck I'll just handwave it as a half action with no roll.

Core, p. 173 (Injector): An injector can hold a single dose of any drug (or toxin), which a character may administer as a Full Action . I wouldn't really modify that, as using Medicae for Space Marines also takes up a Full Action (or about 6 seconds), but of course if it's Super Futuristic Tau Technology, you might change it as you wish.

As for rolls, I don't think any is necessary when a pain suppressor is applied to a willing, cooperative (or just plain unconscious) target.

Thank you very much.