I just added a BN pleco to my tank last week and couldn't find him. Not unusual I know but after a couple days and no luck drawing him out at night I pretty much took my tank apart. If you have a fluval flex, on the sides is the slotted intake, which is fine. Had he gotten in there it's a cavernous area and he'd most likely be fine. However, in the middle is the housing for the pump and it hooks up to the output nozzles. Somehow he got in the output nozzle and couldn't get back out. This is where the water flows back into the tank 24/7. The only time I had it off was tank maintenance the day after I added him. It was off for about 30-40 minutes as I did a 50% change and thorough clean (discovered a struggling Danio) lights off etc, so he either got in there then wanting to escape the.messing around, although the water would have been high enough for him to get in there for maybe 15 minutes before I turned it back on, or he worked his way in while it was running.There's nowhere to go once he's in there except for the tube that hooks up to the pump. I found this all out when I turned my pump back on and it shot out his carcass. That was the 3rd time turning it back on before he was dislodged. So for anyone with this tank or thinking of getting one if you have a BN pleco you'll want to cover those outflow nozzles.