Basement Toilet Gurgling
I recently added a bathroom in the basement which has a shower, sink, and toilet. A washing machine and another sink is also in the basement. When the washing machine drains, the toilet makes a gurgling sound and blows water against the underside of the toilet seat. The water column in the shower drain also moves up and down. The toilet cannot be flushed when the washing machine is draining. The toilet seems to clog easily, something I attributed to it being a high efficiency toilet. I ran an EEL through the main line and found nothing significant. I also ran just the cable from the EEL down the vent pipe and could see the end of the EEL in the main line which tells me it is not blocked. There is a cap at the base of the vent stack. When I remove this cap and drain the washing machine, the toilet no longer gurgles.
The floor drains for the toilet and shower were installed when I purchased the home and have been capped until the bathroom was finished. The horizontal distance from the vent stack to the toilet is approximately 3 feet and 7 feet from the shower. I called a plumber and he said the design of the plumbing underneath the basement floor was installed incorrectly and will have to tear up the newly finished basement to fix the problem. I am not completely convinced that the plumbing design is incorrect, any suggestions?