Hoover agility--poor suction, still!

Hello, my agility has poor suction, it probably vacuums up 1/3- 1/2 of the amount of water put out. I have replaced the lower hose (the short one) b/c it had a tear, and that helped a bit, but not much. I've taken apart and checked all the seals, filters...I've basically taken everything apart except the motor! For instance, with the hose attachment, if I place my hand partially over the intake, water actually reverses direction in the hose. The suction coming from the black plastic part attached to the lower hose reminds me of the first cordless model dirt devil--weak, weak-- wouldn't move a penny from half an inch above it. What else can I check? Help! I'd really like to **** up ALL the filthy water instead of leaving half of it to dry on my carpets and upholstery!! One light-colored footstool (that I'd successfully cleaned before) actually had a dingy spot on it after I cleaned it--from the left over water! I'm desperate for your help...