I have a 2 story home that is 3 years old on a septic system. In the master bathroom there is a garden tub, shower, 2 sinks and of course a toilet. I notcied that when you flush the toilet it causes the water in the sink traps and the shower trap to move a little bit, but the water level never drops or syphones out. If I am draining the sinks or using the shower there is no movement of water in the toilet. Also, when you drain the tub or sink the water drains quickly with no problem and the toilet flushes quickly with no back up.Does anyone know if this is normal, signs of a clog or a possible venting problem? Thanks for the help

This doesn't sound like a problem that will intensify. However, if you're concerned with it You could drop a snake down the lavatory roof vent to check it. My advice? Let it go for now and if you see a further lowering of the trap seals then go up on the roof. Regards, Tom