I'll talk about Sarth first so that your Trash set question can be used to kind of get this post back on track. I tank them regularly and I would recommend a semi-avoidance set. I normally put my normal-MT tanking set on (EH/AV) but switch my Stam trink out for the Dodge trinket while leaving the Repelling charge in. This allows me to jump on Drakes/Sarth with a fairly decent tank set, should the regular drake tank go down or if the Sarth tank is punted out of position. With that in mind... you should be able to do the adds with a BV or AV set... assuming you (and others) stay out of the walls, the add-damage to a tank is minimal.
I have some questions... Wich set for wich situation ?
You speak of a trash set, wich one is it ?
I tank sarth3D's adds, what is your advice ? Avoidance or UH ?