Yep you got it, blocked mainline/sewer. Gurggling downstairs toilet gives it away everytime. You really should consider having an 3 or 4" outside sewer cleanout installed if you don't already have one (NOT the little inch and a half or 2" below the sink window on the wall outside) followed by a sewer cable WITH the proper size blades. Also, I would highly recommend a video inspection run by someone who knows what he's doing and knows what to look for AND can show it to you. Beware the 'professionals'
out there that immediately suggest a section be replaced or the entire line be replaced with little or no proof of it.
If you can't afford the video, etc. be sure to call someone with professional, heavy-duty sewer cleaning equipment that knows how to use it. Assuming your talking about a typical residence with a 3-"4 mainline, proper size sewer cable would be a minimum of "11/16 with either a 3 or 4" set of blades. My personal choice is gorlitz sewer equipment, but I DO NOT recommend it to novices. Do not settle for these companies that show up with a 1/2 inch cable mounted into something that picked up with even both hands. A real sewer cleaning machine weighs 200-300 lbs. Trust me. I use em all the time. If anybody argues with you about that, send em on their way and call someone else. Sounds like this stoppage is only partially plugged so you've got SOME time. Don't wait too long...like till next weekend or later.
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">When
I run the kitchen tap for a few minutes the downstairs toilet goes <BR>"blup
blup blup" with big air bubbles, also after a few flushes the water in <BR>the
bowl is higher than normal. When I check the water level a bit later on
<BR>it's lower than it normally should be. Last week there was a bit of green
<BR>slime in the toilet bowl water. It's clear now.<BR><BR>The drain at the
back of the house has blocked a few times (kitchen tap <BR>outlet to the
sink----<back garden drain.<BR><BR>Also upstairs toilet, but not sure where
that joins, I guess just in between <BR>street ---downstairs toilet/sink
pipe.<BR><BR>What do you think causes are? Blocked sewer drain? I've got a
drain rod <BR>unblocker set but would like not to do that if it's something