I have a conventional sceptic system with two tanks - each serving one wing of my house.

My laundry room deep sink drain has pressure on it, enough to raise the water level in the sink about 10". This happens even when there is no water running down any drains connected to this wing - I even checked the condensation runoff line from my AC drain pan.

When I remove the p-trap for the laundry sink, it trickles "uphill" to where I have to put a bucket underneath of it to catch the water. I had the sceptic tank pumped (which I really needed to do anyway...) and I was sure that the pressure would go away until at least the tank filled up to the drain field exit line. Still water coming "uphill".

Water appears to be graywater - not pure sewage.

I've never been so perplexed in my life. Windyman