Spill No Evil

Solo at level 100:

Few seconds after Brewmaster Bo arrives at cauldron, starter wave will spawn.

Next, you will notice on chat:

Hozen ships appear in the distance!

Groups off Hozens will land at beach. This will repeat 5 times.
Beware! Sometimes Hozen with camouflage will spawn behind you, sneaking to cauldron.

After that, you will get message:

The final wave of hozen ships has come to attack!
Once you have defeated them, help your allies collect Jungle Brew for Bo!

Now you can go into jungle and take your time collecting Brew.

The best way my group found to do this achievement (with lower gear anyway) was to have 1 person running beer while the other 2 defended, took a little longer but was easier to keep the hozen away; they sneak in from the back aswell. I'm sure with more gear it will be fine with 1 person defending.

Can be soloed at level 100.

After a few waves the hozen will stop coming to the cauldron, so just stand your ground for a while first, making sure none of them reach it. And then, when things get quiet, you can take your time and pick up the needed brew, without having to fear the cauldron being robbed while your back is turned.