DIY "pool"

[bphelan19]

Hey guys...
First timer here, and looking for some good help, so hope i can find it here...
I am in the beginning stages of designing a baptismal pool for my church. After brainstorming a bit on what materials to use, cinder block and mortar(with rebar) was a choice... I have a construction background, but not really with block. so, here's the situation:

The church resides in a school, and our sanctuary is in the gym. The pool would sit on the gym floor, so my very first question would be what to use as the base for the pool... We would like it to be roughly(inside dimensions) 3'x7' and 40" tall(having water level around 30". We would also like steps inside pool for ease of getting in and out.
1. is this concept feasible
2. what to use as a base/floor
3. should we use rebar in every other hole and fill all holes with concrete mix?
4. can the inside of the pool be lined with backer board(glued on, screwed in???) and have tile for a nicer touch?
5. do you have to paint block walls with sealer if using tiles

i am sure there will be more questions, but this will be a start.
if anyone has other/better options, PLEASE feel free to share. we are open ears about this.

This will not be permenantly holding water, just on an as needed basis.

draining will be done probably with an item used in draining fish tanks(as i have had for some time now)

Thanks, hope to hear opinions soon!!!

i tried uploading a design pic, but i guess it was too wide, and i can't seem to shrink it, lol...

[bphelan19]

got a friend to resize for me, lol... so this is what i'm intially thinking, minus a floor and tiles inside...