Dissolving Sodium Hexa Meta Phosphate

Hello, 

We have an application where we will need to dissolve 1m3 batches of 20% SHMP. I've read that it's quite tough to dissolve, but if anyone has practical experience with this it would be very useful. 

1. Is it worth heating to improve solubility?

2. Any specific recommendations on design of agitator or mixing tank?

3. What is the best loading system? There are some in-line feeding systems that I've seen, but I'm concerned about hopper getting strangled. So possibly better over just over the top - This has safety concerns. 

If someone has information on dissolving this chemical or similar ones, please get in touch. 

Thanks