According to that site, the hub must be at the lowest part of the bog. During normal
operation, the water from a circulation/filter pump would feed into the hub, to the
pipe, then up flow to the surface. In this mode, there got to be a lid on that hub to
enclose the system. Otherwise, water would not up flow through the hub, and become
useless.

During cleaning/draining operation, the water from the circulation pump is stopped.
The lid would be removed. The water would now down flow to the pipe, then to the hub.
A sump pump is inserted down the hub, to drain the bog.

Ann in Houston wrote:

I am planning a gravel bog addition to my koi pond. I was told about a
filter from Aquascape called the "Snorkel", which is made for this purpose.
Supposedly, you just sink a sump in the clean out once a year or so, and
there is no need for washing the gravel. Here is a link for a similar model
with a diagram. I don't get how the solids get to the clean out vault.
Also, I wonder how the water would disperse to the sides when it can just go
up and then down the slope and back to the pond. They sell additional
slotted pipe sections, to put out to the sides with the vault acting as a
hub, but the base unit is $600.00!!!!!!!! and each extra pipe is three to
four hundred more. And besides, I don't think I want that many hoses going
to this bog. It will only be about six feet wide. I can think of a couple
of different ways to accomplish the settling of the gunky stuff in some kind
of container buried like this one. And if it's successful, I'll sell it to
anyone here for a measly 250.00. I mean, that rubbermaid stuff gets pricey.
; ) Here's the link.

http://www.thepondprofessional.biz/c...roduct_id=1190

If anyone here can help me understand this diagram, maybe a few of us can
put our heads together to do it cheaper, and possibly better. Any help is
appreciated. I am going to also post this on garden web.

Thanks,

Ann