MAy be complicated but I like the idea. Take a look at the following (some photos):
Those buckets (from slucket buckets) have the inlet port at the bottom. During a draining operation, the inlet ports and the return ports serve as the drains. The buckets have a slope and they do completely drain dry (no lip around port).
As long as some time is spent ensuring a small grade on the feed and return lines, you could remove nearly all of the liquid from the system using the same re-circulation pump (and/or by gravity).
The concern I have with those buckets is that, by default, the bottom-side ports are slip fit (unlike proper bulkheads). And, the plastic for these is HDPE. So, being concerned with a potential leak, you’d have to think about ways to ensure the fittings remain tight. HDPE is not conducive to the typical adhesive. You’d need special adhesive intended to bond to HDPE (3M has some). I haven’t had a leak problem to date on that system, crossing fingers.