I remember learning that black soldier flies were in the NW and being surprised that they would live in such a climate. With short, cool summers it must be a challenge to maintain a dense colony. Even in hot climates it can take several weeks to a good colony established, so you might not get good results until next year. Still, any work you can do this year will help expand your knowledge of BSF so keep plugging away.
I agree about reworking the drainage system. That's the weak link in every design I've seen. If I was operating a BioPod or some DIY design other than my own I would add a horizontal slotted pipe over the drain outlet. A 4" round (pipe) or square (fence post) pvc piece with +/- 1/8" wide slots cut into it works well. The slots allow the larvae to pass in and out, which keeps it draining well. That size should be stable enough without attaching it. As with my system, you need some type of bulking material like mulch or charcoal to serve as a filter.
All BSF composters are more or less successful at containing the larvae. I've heard reports of this issue with the BioPod +, and I get occasional escapes with my system too. Since these are outdoor systems, it doesn't matter too much once you have a dense colony and healthy population of free ranging adults. Of course every larva is valuable during the process of establishing the system.
I'm glad you enjoyed this thread. I'm very fond of it because I started it before I had even seen my first BSF.
PS. I've modified my harvest system because some had difficulty with the bag:
