Thank you for your inquiry. If your tank was as full as you indicate, then some of the solids from the tank overflowed into the lateral lines. These lines must be cleaned before any other treatment would stand a chance of succeeding. I know of no chemical which will dissolve this sludge. The only solution is to have the lines jetted or "hydro-jetted" out. This is a process where high pressure streams of water are used to clean the inside of the pipes. The material is "pulverized" into fine particles and washed back to the distribution box where it is removed. After the lines are clean, then the restoration of flow to the drainfield can be attempted. This process can be done by some septic pumpers or sewer line cleaners. 

Septic Scrub can then help here. The biomass around the laterals is probably very anaerobic. Septic Scrub reacts with this anaerobic material to oxidize it and help aerobic bacteria reactivate. 

Wit regard to perk testing, the response to the previous article, Wet Areas, gives a method for testing the adsorption ability of a drainfield. You can try this at anytime, but based on your inquiry, I am sure that it would fail if done before a drainfield treatment. 

If you have any additional questions, please do not hesitate to call.