Depends primarily on where the tanks spawns - if it's on say BH4 down by the warehouse, set up in there with gas cans/mollies/petrol tanks ready to whack him if he goes for the forklift and wait him out until he swaps to AI. If he goes in, maneuver around the tables while hammering 'im.
In levels where you can easily and safely retreat, like BH3 trainyard (run back to the stairs, run up the stairs and even farther back until tank dies) that is certainly the best option.
Finally sometimes you just have to kite him around outside while hammering him and using cover (BH Finale, DT finale, NM finale, actually all the finales, as well as parts of DA2, DA3, DT3 and DT4).
Pardon the long explanation, in a competitive clan here so we get pretty into it

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