Well they both work. The spray can be used on new goo puddles for now, so only those left behind by enemies or you, not default ones. The yellow medkit is going to be reworked, but it works by removing the horny/drone state i.e. the thing that prevents you from using a blue medkit and changes your thought bubbles.
I actually had the same idea with shooting that tank, but much like with everything else run out of the time before the release. It's still early in development so I will probably add it one day. Cool to see someone else thought of it!
Viewing post in Aftershift: the Post-TF game comments
i haven't seen any tf prevent me from using a medkit, odd. the white wolf one just let me use normal medkit, and doesn't seem to have any odd effect overtime.
only thing i seen that had hypno was the pig, but it was short lived because i got stuck trough the wall... also the ball that teleport you to the conveyor need to be made smaller to allow dodging, and with a shorter hitbox (it genuinely un-avoidable, making me require to spend bullets on them just to try other tf or interactions).
It's not TF, it's the horny/drone state that prevents it. It's triggered per form differently. You can temporarily use animation speed up to overcome this bug, just use interaction key 5 or "b". The servitor is purposefully large. If you really don't want to spend ammo you can lure them into a loop.