A sponge typically increases the surface area.
Some people use jar lids for their water. They keep trying different size lids until they find the one that gets the humidity right for them.
Do not close the vent plug. They need more oxygen while hatching than at any other time.
Control the humidity by controlling the surface of the water. More surface area = higher humidity, less surface area = lower humidity. Never use the vent to control humidity.
If they don't have any cracks they are unlikely to explode. It isn't uncommon for there to be some that are cracked during shipping. Cracked eggs are very likely to explode. I never intentionally set any cracked eggs.
@Kiki used to candle every day. As long as you don't keep the incubator open too long at a time, it does not hurt anything and may actuaslly help. Broody hens normally get off a nest every day. I had broody chicken hens that would get off their nest every day for at least 15 minutes. They...
Hammer drill is faster and keeps the bit contact area from glazing which makes the drilling take longer. Concrete blocks should drill just fine with a normal drill and a masonry bit.
One more item is that hatching eggs can be shipped via UPS or FedEx.
One of the worst things for hatching eggs is to be shipped by air in an unpressurized cargo hold. The changes in pressure due to the changes in altitude can destroy them.
Given the choice, I have hatching eggs shipped by...
They're all bad but less can happen to it sitting there waiting for you than the additional transport and final toss delivering it to you.
Some of the harm is unintentional such as sitting hatching eggs by a heater duct to "keep them warm".
My experience is that eggs that come through a major...
FYI, if shipped eggs do not develop, it does not necessarily mean they are infertile. Eggs that go by airplane in a non-pressurized cargo bay can be destroyed by the changes in altitude. They will not develop even if they were definitely fertile to start with.