This is my proposed solution for the notorious problem with Ryobi's backpack sprayer.  The model number is P2806BTL.

When you get down to the lower portion of the tank, the wand looses pressure and it throws off fertilizer applications.  I believe most people are just dealing with it in some way, maybe mixing a little more product than needed to account for the lose in pressure when the tank is low.

This is designed to go over the existing filter and force the pump to pull from the bottom most portion of the tank.  I have concerns with covering the filter and overloading the motor, but I am also tired of having a little bit of yard left and loosing all pressure and I don't want to mix more than I need so I am going to risk it.

I will update this if anything negative happens, but for now, this is getting nearly all the fertilizer out!  

USE AT YOUR OWN RISK!