I'm about to start planning the black science but a problem I've had since a long time ago is over-saturation of Sodium Hydroxide. I've been stockpiling it thinking it would be useful later on but now I'm thinking whether there is a way to void it that I have not noticed.

So what to do with hundreds of thousands of stock-piled sodium hydroxide?

Caustic solution is voidable in an outfall.

That makes sense. I avoided that route because I felt it was wasteful compared to sludge and wastewater treatment, which usually yields some byproducts that you can use for other things.

Thanks for the input. BTW, is there a way to calculate how many sterling engines can a 2x2 reactor feed? I currently have 20 per side, but I'm thinking it has capacity for more.

The reactors tell you how much thermal energy they can generate, and make sure to include the neighbor bonuses. Tier 3 stirling engines produce 8MW of electricity at 95% efficiency. That means they consume 8MW divided by 0.95 or around 8.42 MW of thermal energy. So however much your reactor generates, you can divide that by 8.42MW to get the number of stirlings it can support in equilibrium.

However, if you have any sort of variable power generation like solar or wind, that will take precedence over the stirling engines. It may make sense to slightly overbuild the number of stirling engines so that you can take advantage of the heat that builds up in the reactors when the energy it's being fully utilized and over-produce electricity from your reactor when winds or solar are down. So there isn't an objectively precisely correct ratio of stirlings to build.

The throughput of heat transmitted from stirling to stirling is not as effective as heat pipes, so there is a limited number of them that you can chain directly together. The exact number varies by tier, but it's closer to 2 or 3 than 10. Just FYI in case you were planning on connecting them directly to the sides with no pipes.