h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I decided to change the covers on my septic tank.

Whilst clearing the earth around the four covers I found beneath the grass and weeds two vertical pipes which looked down into the chambers.

Both have earthenwear stoppers.

The system was installed twenty years ago and is working efficiently.

Can anyone suggest the pupose of the 4" diameter tubes or can I bury them again?

Thanks

Could the holes be for visual inspection?

Or maybe lifting points to lift the lids?

Or a vent?

Or an access for monitoring the scum level. Can you poke a stick in it?

Here look at the top of page 5.

http://www.p2pays.org/ref/17/16670.pdf

Thanks very much for your suggestions.

I suspect the viewing holes is the answer as each is above a transfer point of content from one baffled area to the next.

It has also been suggested the acess pipes could be used to clear any obstruction but I think the manhole covers, which are quite close, would be easier for that purpose.

Thanks.