RTB, thanks for the info.

The top of the tank needs to be just slightly higher than the water level of the pond.

Is that the only option? My bottom drain is plumbed running
underground until it gets to the pump, filter & UV in a utility area
in my basement which is below top-of-pond level. There's a drain there
for waste, but again, the area is lower than you're saying. If I had
this outside, I'd need to dig down maybe 6' or so to reach the current
line, cap off the drain in the pond and cut/replumb the line. That's
quite a bit of work, plus it would bring my line above the frost
layer, so freezing would be a problem in the winter (I'm in NH).

Why does it need to be placed above the top of the pond if the water
is being pulled through it by my pump? Can't I just shut off my pump
and close ball valves on either side of the tank in order to inspect/
empty? That's what I'm doing now.

Also, can you see in these types of tanks without opening them? 55
gallons makes me think of a big oil drum. If I had something like
that, I'm not sure I'd even know if fish were in it.

Thanks,

Dave