Help with a student project - subtract or other tool for removing multiples

I’m guiding 30 8th graders through their first attempt at 3D printing. I’ve got this file of a little container - all the cylinders in the top are there to try and use the subtract tool to punch out holes.
First, I see that the “back” is not a solid so you can’t click solid 1 - solid 2 to make them punch out.
Also, I know there is some type of array tool or method to create multiples like this, but that’s not in my skill set yet. Any tips or anyone able to make a couple changes to this file to help me teach better?

Allies final.skp (195.4 KB)

you would need to make the main vessel a group for the solid tools to work. the cylinders should pass all the way through to be sure they intersect properly.

It may of been easier to array the circles on that face and just push pull the holes?

also, once the main vessel is solid, you could group all your cylinders and punch all the holes at once.

as for arrays, you can make your circle and then use the control key when you move it (“+” icon will appear) and you can move it the distance you want the spacing and immediately type " * " (by the number of instances of it you need) or you can move it to the furthest position and use the divide “/” and number to place holes evenly divided between the two, as I did here (not that accurately!!).
Then select all the hole outlines and copy those down by the same technique. Push pull one hole and inference the back face for the correct depth, then double click each hole with the push pull and it will copy the push pull amount on each one.

when laying out the hole it might be useful to layout some guides to keep everything where it should be.

! wait for it


Thank you VERY much!