I have an odd problem that I will try to explain the best I can. I have an old one bath rental house that was built in the 50s. The toilet does seems to flush waste fine, although it empties the bowl, it does not have a very strong flush at the very bottom of the process. It seems to leave about 2 of water in the bottom of the bowl (this may or may not be an issue since it is an older and/or cheap toilet).
When the toilet is flushed, water rises in the bathroom sink vent pipe about 12 above where the sink drains into the wall. Let me explain: In the closet behind the bathroom sink there is a 2 old galvanized T that the sink drains into. The previous owners had taken off the vent pipe and replaced part of it with about a 2 PVC section that does not fit the galv T. So with the upper vent piece that runs up through the roof off, I can see water rise about 12 above the T in this vent pipe when the toilet is flushed. After 20-30 seconds it does slowly drop below the floor. I am going to cut out the old T and correctly replace it and the vent.
There is one P-trap under the sink. I cant tell, but there may be an old galv P-trap under the floor of the bathroom sink. I assume if there two P-traps that could be on issue. On the tub side, the tub drain goes into a galv T and drops about 16 into a galv P-trap. There is only this one trap, the galv one. I removed the vent pipe at the T for the tub drain (behind the wall) and the water stays below the T when the toilet is flushed.
The toilet and tub are next to each other. The tub does drain slowly. The bath sink if I leave the water on full for a minute will start to back up into the sink bowl. It does slowly go down and drain. I have flushed the bath and tub lines with a bulb flusher (I know, I know, thats bad) and the water does drain. When I did this water did not seem to back up in the vents or toilet. Water does not seem to be bubbling up in the dirt under the house under any of the drains.
So, the questions are: do I have a partial blockage in the 4 toilet line? Do I have a venting problem? Do I have a some kind of blockage in the bath sink drain line? Do I have a venting problem?
Sorry this is so long!! Thanks in advance!!
If the water is not going down the drain just as fast as you can put it in, the drain is partially clogged.