as the cement was poured and vibrated in.
When we built our place, we had a LOT of blocks that we were going to core-fill.
We knocked the bottom out of the blocks so we could wash out the morter that inevitably gets in the middle that would have made it hard to put rebar and concrete in later.
You get an idea of the number of holes to fill - this is part of one wall!
The guys busily making sure all the rebar was in and facing the right way, and watering the blocks before we poured concrete in
Thank goodness for concrete pumps!
I can't find the picture I wanted - of the guys lifting concrete a bucket at a time to pour into a couple of blocks they missed!
Anyhow, the other thing I was going to say - don't over-vibrate the concrete in those blocks. They're fairly brittle, and if you vibe to much - they burst! Fortunately it didn't happen to us, but I saw another site where they did - and had to pull down a months worth of work to fix it!