I have a Gerber 3.5 gallon toilet in a small outdoor bath that won’t flush completely. The toilet was there when we bought the house and I just realized that there is no vent stack. The water siphons out of the bowl very rapidly after flushing. It will flush completely if you pour 5 gallons of water into the bowl so I don’t think that the line is blocked. I’ve cleaned the openings under the rim. There was some build up in them. I tried to snake the small hole below the water line but the wire only went a short distance straight up then stopped. Which way should it go from there? Will this toilet ever flush properly without a vent or will I have to install a stack? There is no sink or shower just the toilet.
The problem may just be in your toilet. How high is the water level in your tank? It should be about 1″ maximum below the top of the overflow – The lever handle chain may be too long, causing the flapper to close too soon as well. these are a couple of things to look at before ripping into your walls to vent your toilet. However, all toilets (& all fixtures for that matter) really should be vented.