When we run water elsewhere in the house - the water level rises quickly in the toilet.

1. The main line is clogged, you need something like Roto-Rooter to clear it, a snake won't cut it. The toilet is the clean out.
or
2. The drain field is plugged. Backhoe and trucks and lots of money.

I've kept working on it and now other water in the house can run without that one toilet's level going up.... thats sort of good I think - but I'm still going to keep a very close eye on it.

Still probably going to need a drain cleaning service though unless it clears up overnight!

UPDATE - it's only slightly better this AM - water is clean and goes down the drain but ever so slow. I'm continuing with hot water and Dawn and plunger but so far no sign of remedy.

UPDATE II - I had it running again, but then when I tested it with full force water down the drain from the bathroom sink and kitchen at the same time - it slowed down again. It's like they pushed something back in the way. Upstairs water running no longer affects the toilet water level however.

This post was edited by karyn on Thu, Dec 20, 12 at 8:46

Sounds partially clogged.
If the obstruction is after the vent for the toilet (the line out to free air) the plunger cannot develop any significant pressure.

Thanks all - it was never DIY - we ended up calling the plumber and they had to remove the toilet and snake the drain - the obstruction was WAY down the line - 60' or more - almost to the sewer. It took two passes to clear it. And about 2 hours @ $90/hour Plus+ Plus+ Snake Fee $75 - Plus+parts and tax.

$288 total - worth it IMHO to know it's done - and done right. Whew - a relief that this is over.

We've only lived in this house for under 2 years - plumber says this was something that started happening long ago.