How to get sealant out of the radiator
Drain and flush the system.
If a standard flush doesn't work, a radiator shop may be able to back flush your radiator and salvage it. I would also worry about how much of this sealer is in the block and heater core. Some of these products can be downright nasty, and screw things up very badly. Hopefully your radiator can be salvaged and you have no other issues with this bad stuff!
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