I assume that when you had the leeching tanks pumped , the pumper removed most of the solids. Before they fill back up, you can try to wash the side somewhat and then add two bottles of Septic-Scrub the first day and two more the second. There should be enough water in the pits to dissolve the product. You should then moniter the pits and when they fill to about 40%, another two bottles of Septic-Scrub can be added. This is to try to control the build on the bottom which is preventing the pits from draining. 

Please do not hesitate to call if you have questions.