Large plexi reservoir for multiple submersible pumps

[Karantanec]

Hello and greetings to all.
My first post on this forum and hoping to get some valuable advice.

I'm making my first WC project for two PC's with 2 separate external cooling loops (1/2" tubing and fittings, used car radiators, multiple blocks in both PC's) but a large shared reservoir with 2 submerged pumps in it (Hydor L30).
I'm going for a passive cooling with no fans inside the cases or on the radiators.
The goal is silence, not overclocking.

How do I seal the reservoir top and bottom (a long standing plexi tube) and 4 fittings in such a way, that everything can be easilly dismantled and replaced (that means no use of glue and adhesives).

I expect the size of the plexi tube-res to be about 600-700 mm height, with 5 mm thick walls and an outer diameter of 180-200 mm, effectively making up a volume up to almost 20 liters.

I will post more details if asked, but that's the general idea.