I have a ranch house with two baths back to back. Majority of piping comes together in storage closet in basement which allows fairly easy access and visibility. We had a 1000 gal septic tank installed about 6 yrs ago and had it emptied last yr. The smell of sewer gas is very strong in closet and in main bath especially when showers are used, main bath has double sink and laundry chute which allows more openings for gas to rise, master bedroom bath has single sink that is pretty well sealed. I tested by using one shower one day and the other the next day and got the smell both days--do not have any tests on toilets, don't seem to smell it before taking showers and having used toilets. I have a friend who is a general contractor and he looked at it and said no visible cause, could be I need to replace wax toilet seals. There was no smell a couple weeks ago when we had the very warm 3 days, and none this past week one day it was in the 40's, as soon as it got cold again, smell came back. I thought it might have something to do with roof vents, any suggestions or should I replace wax seals?