Distilled White Vinegar, at Safeway for around 2-3.00/gallon works great, you have to get it into the pump, then run it through ALL your extractor tools so it helps clean them out, leave it all overnight, and then run clean water through it..
I have never purchased their system maintainer and almost a decade later with years of hard use, its still all original in there and all my tools are not clogged..
Make sure your water tank is clean and not full of dirt, then pour your chemical in there and fire it up..
Of course, it will be in the hose and hopefully, it will help clean out whatever is in there...
Good luck,
Dan F