Whatever you do the more filters you have the better. It means that you can use the same solvent to wash them all (raher than doing them one at a time) and have a 'batch' in bags ready to use . This is saving money on solvents.
If you doubt the effectiveness of washing in hot soapy water after the initial solvent clean, then try this-
Clean as you would with Solvent.
Run a hot bucket of water with washing up detergent in it.
Wash the filters in this by squeezing them under the water 5 mins (keep this bucket of water)
Rinse in fresh running hot water to rinse out the detergent.
Hang up to air dry (this can take a while in cold/damp climates, in the house is good but they tend to stink a bit!)
Now go back to that bucket of water...very gently pour off the water and look at the amount of sand and grit that has settled in the bottom. I bet it will be there, this is why I follow up a solvent wash with hot soapy water.