When I accumulate a significant amount of water in my tub and then release the drain, it drains normally for a fair period of time. Then it slows down (or stops) for several seconds and then starts draining normally again. This repeats itself several times until all the water is drained out. My home warranty company sent a plumber out who said that the problem is that the drain goes down to a P-trap and, when it comes out of the P-trap, the drain line goes slightly upward until it dumps into the main sewer line. The plumber explains that the line probably goes slightly upward because it used to have a drum trap that was removed. This explanation does not seem right to me for the following reasons:
1. The point where the tub begins draining (i.e. the drain plug at the base of the tub) is at a point higher than the point where the drain line ultimately dumps into the main sewer line. Therefore, the overall flow is downward even if the last part is slightly upward.
2. If the problem were the slightly upward flow at the end, it would seem to me that the tub would drain consistently slowly, not drain at full speed, stop up for a few seconds and then drain at full speed again.
What do you all think? If you disagree with the plumber (who, by the way, is incentivized to blame it on the installation because it gets the home warranty company off the hook), do you have any other ideas of what could cause this type of symptom? Does it sound like a venting issue?
1. The point where the tub begins draining (i.e. the drain plug at the base of the tub) is at a point higher than the point where the drain line ultimately dumps into the main sewer line. Therefore, the overall flow is downward even if the last part is slightly upward.
2. If the problem were the slightly upward flow at the end, it would seem to me that the tub would drain consistently slowly, not drain at full speed, stop up for a few seconds and then drain at full speed again.
What do you all think? If you disagree with the plumber (who, by the way, is incentivized to blame it on the installation because it gets the home warranty company off the hook), do you have any other ideas of what could cause this type of symptom? Does it sound like a venting issue?