Weird drain design

I replaced my soil stack vent with an air admittance valve, but when I flush the toilet the water doesn't go away so quickly (only an extra 2 seconds, but the flow now isn't fast enough to clear the s*it and some floats!) and also I can hear it pushing into the nearby shower drain. At the bottom of the soil stack is some water, as though perhaps the pipe running from there to the main drains is not entirely downhill. I assume it's creating back pressure. If I flush the toilet with the vent removed, it flushes fine. The toilet is only a couple of feet from the soil stack.

I had a peek in a drain cover just outside the front of the house, and there are two drains, one for waste, and one for the gutters. The waste drain is blocked, it's full of water there. And simply flowing over into the rainwater drain! How stupid! So I've been polluting the rain drains all this time without knowing. I guess I go borrow a big drain rod....

The manhole at the bottom is clear. The blockage is between the two, I assume you push with a rod, not pull, so I'd start at the full one.

Surely moss can block it anywhere along the pipe?

tree roots?

Closest thing is a laurel hedge. But that's 2 metres away. The inspection cover at the bottom of the garden revealed a small pile of soil. I have emptied the contents of a wet and dry vacuum down the toilet many a time....

I meant having been washed off the house roof.

IIRC recent regulations made the clearance of blockages on private drains the responsibility of the local water co.? Malcolm

Really? Surely if it's on my property it's nothing to do with them. Or is it like with the electric company, it's theirs up to the meter?

Looks like England and Wales only, I'm in Scotland:

That only applies to sections of drains that are shared by more than one dwelling or are beyond a property boundary.

I just watched their video for a detached house, and all they've done is take responsibility for the small little bit of pipe under the pavement! As soon as it's under your garden, it's still yours. I thought they already had responsibility for the pavement bit, but apparently it used to be done on where it joined the main sewer, not by property boundary.

The S might get blocked quicker, and not have had a chance to set hard.

I didn't read far enough and took Malcolm's word for it. All they've done is take responsibility for the bit of pipe between your property boundary and the main sewer. Mind you, property boundary in legal terms includes the pavement and the road, even though the council are in charge of it!

when tree roots get into the drain.

If your surface water goes to a soakaway, the foul water/s*it may well block it up and be expensive to fix.

Unless tree roots have got into the drain. Or the drain is badly laid/installed. Blockage can happen anywhere inthat case.

Or if the drain has backed up due to a blockage elsewhere.

If the blockage is not on your property, get the people who own the drains in your area to come and fix it. Brian

Strangely some places to have one big cover out in the street with both in there a small distance apart. Probably not the done thing nowadays, but have you not ever wondered about hose reports of sewage coming up drains? Brian

I imagine it joins the street drains.

It is, it's under my front garden between two manholes. They're only a few metres apart, so the blockage should be easy to shift.