if you go to the pool shop you can purchase, very VERY cheaply, bulk bags of sodium bicarbonate ph buffer. this reacts with hydroxide to form nice safe only mildly basic carbonate, and it doesnt foam up when you do it. This can make it a lot safer to store the soup in things like plastic bottles or drums pending a better method of disposal if you cant flush trace naptha or hydroxide down there, though you usually can, this isnt even very concentrated sodium hydroxide, its likely no different than what is normally present in stabilized bleach cleaners