Ubogri will put some of the purified water into the green whatever.

You try moving the vat but it's too heavy, your only option is to use something else to pour the water from vat to vat. 

"We can see if the containers in this room were warded enough to contain the vile liquid." Lumiere suggests. She'll collect one of the clay pots and one of the old jars from the side, and then hold the top of it and attempt to dip the tip of it in, seeing if it reacts with the liquid before submerging it.

 When the jars touch the green liquid nothing seems to happen. 

"I suppose it would be slow, but we could decant with these into the emptied vat." Lumiere gestures to the one that the ooze was sitting in.

Ubogri helps Lumiere.

Sounds like it will take a long time but sure, let's do this thing. We use the various pots, and whatever to empty out the green stuff into the now empty slime vat.

If it takes a while, I guess the others can short rest while Lumiere works on it.

I think we're all working on it.

Found some maps I can post to you! 

You manage to empty the vat. It takes a long time since there's a lot of stuff inside and sometimes the contents come in contact with your skin damaging you. At the bottom of the vat you see another half of a key, this time it's the tip. It's golden and very shiny and it looks like the liquid had no effect on it. 

(Just checking who 3 and who 1 is.)

Quote from pokepaladdy >>

(Just checking who 3 and who 1 is.)

I went with your order. 1 - Lumiere, 2 - Ubogri, 3 - Jerigg

Hm... I edited it but dndbeyond didn't update it, weird. 

Edit2: No, the edit was actually there. Very strange but w/e

Lumiere takes a little abrasion damage from the acid, but seems to care little. She looks to the others. "Shall we utilise that mage hand to collect it, in case of any other dangers we are unsure of?"

“That seems to be the best strategy.”

"Is being good idea," I get the key bits and put them together with Mage Hand.

"Is probably another trap..."

You safely take the key out 

"We appear to have found two pieces of a puzzle." Lumiere states, looking at the two pieces of the key. "The mention of keys was prevalent within the riddle at the entrance, so keep a close grasp onto those pieces." Lumiere offers a scrap of cloth to potentially wipe any remaining acid off of the key pieces so they can be carried with little issue.

Do the pieces connect to each other? If they do, I put them together and see what happens.

Are there other ways out of this room?

Investigation0

(Might wanna do that with mage hand, just in case.)

Falmo will drift into the shadows, just in case it spawns an enemy or something.  He will stand ready to loose an arrow.

Stealth: 18 or 25