With 25lbs of grain and 6-7 gallons of water its FULL. I mean absolutely no more water going in there haha. If I can't figure out my issue Im going to buy a Big Blichmann pot.
An issue I have with large grain bills (25 Pounds) in a 10 gallon Igloo is not enough water flow through the grainbed to keep the suction on the pump wet and the element cool. I think it maybe due to my crush but I am going to adjust my mill the next big beer I brew.
Throttling any pump on the suctions side without knowledge of the process and mechanical functionality of the pump is a bad idea, and will lead to damage of the equipment. You should always in this case throttle with the discharge of the pump.