Plumbers need to know this so they don't get burned when they remove your pipes. They have industrial augers (snakes) that will physically pull out whatever is blocking the pipe—something chemicals cannot do.
Use a small cup or a wet/dry vacuum ( rated for liquids ) to remove the neutralized water. Dispose of it down the toilet (lots of flushing water) or outside away from pets. drain blocked with caustic soda
Put on rubber gloves (dish gloves are fine), safety goggles (not just glasses), and old long sleeves. Caustic soda burns are no joke. Plumbers need to know this so they don't