I need a little schooling on Jetter/Vac trucks

Vacuum Truck Experts,

I need a little schooling on Jetter/Vac trucks,

I don't want to sound like an idiot ! but i'm going to anyways

The folks that work for me here has convinced me that we need to purchase a Vac truck. First of all we will mainly be servicing ,Lift Stations,Catch Basins, jetting service for storm water inlets/Lines.

So I'm thinking along the lines of a VAC-CON Vacuum/jetter combo. 10 to 12 yard.

Now some of these Lift stations we own have a depth of 30-40 ft, when i'm  looking for a truck what do i need to look for in regards to vertical suction power to insure we can pull the muck/water that far without loosing suction ? I like over kill with everything.

Also the filtration systems they talk about on some vac trucks, What can they filter out? Do they have the capability of filtering out Oil/Grit or the Hydrocarbons from the water we suck up, discharging clean water into the tank? or are they just referring to filtering dust when excavating?

If you-all could take the time to suggest what we need to look for in a truck and also what to avoid i would be in debt to you,also my budget will only allow us to purchase used. 

              Thanks