[Sharp_Enderman]

So I got a spider grinder up and running, but I've run into a particularly annoying flaw. I just can't manage to hit the spiders with an instant damage potion. I've gone through at least 30 potions just trying to get it to work. I've removed various bits to expose as much of the spiders as possible without allowing them to escape and I still can't manage to get it to work. A dispenser works wonders, but that doesn't make the spiders drop experience.

The original setup without any blocks removed to give me additional access to the spiders.
java 2013-07-14 21-20-14-47.jpg (134.29 KiB) Viewed 723 times

Any help would be immensely appreciated. I'm at a loss.

[Yeavon]

use a half slab instead of the one glass block?

[Wxclm]

Is your pvp on?

[Sharp_Enderman]

PvP has no effect. I shall try the half slabs.

Edit: The half slabs did not work, unfortunately.

[cobaya18]

PvP has no effect. I shall try the half slabs.

Edit: The half slabs did not work, unfortunately.

It didn't work.

[Life_is_a_party]

PvP has no effect. I shall try the half slabs.

Edit: The half slabs did not work, unfortunately.

PVP does often have an effect even against just mobs while it is disabled and using splash potions.
Try enabling it before using one, as I know it causes problems with weakness potions against villager zombies.

[Sharp_Enderman]

PvP has no effect. I shall try the half slabs.

Edit: The half slabs did not work, unfortunately.

PVP does often have an effect even against just mobs while it is disabled and using splash potions.
Try enabling it before using one, as I know it causes problems with weakness potions against villager zombies.

Already tried having PvP enabled while tossing potions at 'em. Had no effect. I can also hit the freshly spawned, not bunched up spiders with the potions perfectly fine even without PvP enabled.
I have a feeling it has something to do with how small the opening is. I can throw a potion and visibly see it land somewhere I blatantly wasn't aiming. Even when I'm right on top of the spiders, looking straight down, the potion seems to land just above the spiders or veer violently off course and hit a wall for unknown reasons. I've also hopped in with the spiders so my feet where on the same level as them and the potion still had no effect. I intend on trying to get it so my head is on the same level as them and seeing what happens then.

Edit: I just got my head on the same level as them and it appears that it'll work. I shall bunch some up and report back shortly.

[Sharp_Enderman]

Well I've gone through another 15 potions with a multitude of different combinations for block placement. Still no success. There's just something about them being bunched up that the server disagrees with, thus I can't manage to land a successful potion on them while they're clipping so hard.

[Tyranitar140]

I would suggest breaking a hole in the ceiling above the spiders and putting a trapdoor over it. Then, when you want to throw the potion, you can just open the trapdoor and throw te potion down.

[Sharp_Enderman]

I would suggest breaking a hole in the ceiling above the spiders and putting a trapdoor over it. Then, when you want to throw the potion, you can just open the trapdoor and throw te potion down.

Tried something very similar to that. Still couldn't get the potions to work properly.