My advice:

Eck - when I followed some of the strategies on the videos, I still would get the random aggro dump problems which would result in an occasional wipe. I did the "magic distance" trick and now it is EZmode. The "magic distance" is the distance your DPS has to be from Eck in order to prevent him from aggro dumping and jumping to the new aggro target (usually DPS). If you look at the floor, there are 2 piles of bones a ways away from the entrance to Eck's lair (where cave turns to a stone hallway). I usually plop my shaman about halfway between the two bone piles and then tank Eck halfway into the hall. Basically, position your tank where you are planning on tanking Eck and check the healing range. Then. once engaged, if you are OOR of DPS spells, you can inch forward until you get into range.

For the Colossus, it is highly recommended to use nature resist if you have it. Some people advocate strafing to avoid the pools but I tend to just heal through it. Of course healing through it is easier with Chain Heal x 4.