The bath and the wash basin have been very slow to drain.
I mean very, very, slow!
I called a plumber.
Tom came and I showed him where I thought the grease trap was. Uncovered, it turned out to be an unlined hole...and dry. Mmmm! Tom located the actual grease trap near to the house.
Check this out! Pity you can't smell it!
It turns out to be an old concreted laundry trough - repurposed. So, no fancy sullage treatment here. The kitchen and the washbasin drain into the grease trap, which overflows into the other pit (well it does now the pipe is unblocked) and soaks away.
The bath water just disappears somewhere under a large concrete slab. Now with a bit more forensic plumbing we could probably locate this, but as it works, we aren't going to try to find out unless there is a problem in the future.
In addition, the pump on the house tank is leaking and Tom just laughed when he saw the fixtures. Basically, it looks like somebody had shares in a garden hose factory. Even the toilet is plumbed using garden hose. He is coming back to replace some spouting and fix the leaky pump.
Here are some pictures to help take your mind off the yucky grease trap.
You've got to love spring!