How to Build a Septic System

Other than the usual way, I haven't a clue.

ok, it's slow. i'll bite...

which usual way is that?

I have a book called Septic Tank Practices. Seems very hands on or feet first. Peter Warshall the author. It's one of my treasures to hang on to, but maybe you can find a copy, or something similar online. (That book was published in 1979).
Or... wiki.

Sawdust toilet
http://humanurehandbook.com/

Ah, an expert shows up..

I am no expert!

I would look at a large system, "say about 750 gallon tank which would fill up in a week under normal usage and then think about how much water you will be walking into your camp site in a week and then devide that into 750 to find out what your tank size should be and the actual drain field would need to be in comparence.

Keep in mind that I am no expert and good luck

First find out what town planning laws might need to be complied with.
My preference would be a septic system however this will involve digging a bloody great hole and installing a concrete tank and realm drains. In the future septic sydtems might also need pumping out, usually by a waste collection service.

An alternative might be a composting toilet however my personal experience with these are that they are not that effective. Ie build it well away from the dwelling.
Composting toilets are often used as an alternative to central wastewater treatment plants (sewers) or septic systems. Typically they are chosen (1) to alleviate the need for water to flush toilets, (2) to avoid discharging nutrients and/or potential pathogens into environmentally sensitive areas, or (3) to capture nutrients in human excreta. Several manufactured composting toilet models are on the market, and construct-it-yourself systems are also popular.[2]

Right, good idea, dp.

composting toilet - expensive to buy, but cheap to keep.
http://en.wikipedia.org/wiki/Composting_toilet

digging big holes is not a problem.

buying big tanks is...

for legal purposes this will be considered a temporary structure...

Perhaps thats to do with set up and maintenance.

I just found a dozen or so ways to build a septic system on internet. It's just so involved: the pipe to have the water run out from the house, the tank it runs into, then the field where all the stuff goes to. I've had 3 homes with septic tanks. Do you plan to build your own septic? Mighty ambitious project, mighty brave person, Rockhead

dog bless canada and all of her people. even the simple ones.

I think this sawdust turlet idea might be a winner.

the rest of the waste water could run into a pond. it would mostly be kitchen waste, and I can get organic soaps...

brave and desperate are close cousins...

and then there is the leachfield thing.

It's been a while since I considered any of this. Is this in a county jusridiction? See if there is anything online (I suppose you already have) from the county site.

and then there is the leachfield thing.

It's been a while since I considered any of this, usually as a fait accompli. Is this in a county jusridiction? See if there is anything online in the county department of whatever... (I suppose you already have).

Organic soaps are our friends. (Dr Bronner, maybe?)

A quick look around the web tells me a composting toilet will cost anywhere between 1000 aud to 4000 aud. Building away from the dwelling would be problematic given your winters, also a problem for the decoposition process I feel. Building high enough to provide a chamber below could also be problematic
Septic system will cost something similar (say arounf 3.5 k AuD)

there is a chamber below.

it is an elevated cabin...

and I'm real handy, jack.