I also have "plugs" for my drains, just in case I ever need to completely shut them down. I've mounted the plugs to PVC pipe so they're easier to use, but to your point, most of the time, you could just use a longer piece of PVC and bring your drain pipes up high enough that they drain out completely with the return off. I've got a one-way valve and then a shut off valve right above my return pump as well. I like the redundancy. The one-way valve I got is a PVC ball that's set completely in dark PVC so that there's no algae growth, and it's also got unions. I'll probably clean it once a year, and my only complaint is that the ball floating on the inside is a bit noisy, but it's less likely to fail.
Looking forward to seeing the final build.