The burrowing worms increase the aeration of the soil to improve water absorption. I haven't done this yet, but my research as listed in my report proves that worms are extremely effective in the drain field.
https://docs.google.com/document/d/1HL-0iahk8hPwqclnajsgFnaDEq6JGNMZLaCZ14c2rps/edit#

Will worms survive copper sulfate added so frequently to the field? I don't know. I would strongly advise checking with local authorities before doing it. This stuff can't be removed during the normal process of treating waste water. It could end up back in your drinking water.
Also...putting it in your septic system is just going to kill all the natural organisms and bacteria that have to be there for the septic system to work properly.
Really do your homework on this stuff before you use it. If you go ahead, Copper sulfate should not be added to the tank, but should be added to the tank outlet pipe or to the D-Box.
http://npic.orst.edu/factsheets/cuso4gen.html

IMO, the best investment is to add risers to the tank & to your D-Box to make future maintenance fast & easy. Hydro-jetting the laterals and pumping the tank should be an easy chore as needed. Hydro-jetting the laterals will also blast away roots. Risers above the tank will make it easy to measure sludge levels in the tank so you don't waste money pumping too often.

Grizz