Toilet empties when showering
We have a septic tank. Our house about 35 yrs old. I've noticed the past couple days our toilet in out master bath has been mysteriously empty when I go in the room. We have 2 bathrooms, back to back. Today I took a shower in that bathroom and heard "bubbles" and noticed the toilet water level going down while showering. Do we need to have our septic serviced? Was last serviced 5 yrs ago.The yard where the tank is odor free and dry. There is no odor in the house. We live in South Florida. Thank you!