There's no need to disconnect or drain the loop for hardware switches on an open bench rig (disregard advice if you're in a case).
This is what I do for the ole rapid switcharoo:
Rubbermaid container as a
shared res for 2 loops.
Loop #1: D5 Vario/GTX 480/Stinger V8 CPU block (center inlet - dual outlet)/res
Loop #2: D5 Vario/GTX 120/Enzotech Sapphire NB block/MCW60/MCW60/MCW60/res.
I use long tubing for both loops (tygon 7/16 id 11/16 od from Gary) and keep all the blocks attached permanently. With the long tubing, I just use whatever block(s) I need and set the others out of the way. I rarely drain the loop (just for cleaning) - and the Rubbermaid container makes it a piece of cake.
If a pair of disconnects costs $40, then you're better off just having a bunch of MCW60's permanently attached.
Here's a submission with a bunch of the blocks in use.