The last few months, i've noticed a strong sewage smell coming from my bathroom sink. i live in a house built in 1924 - ranch with one bathroom. it seems to happen whenever you run the water - you especially notice it at night when brushing your teeth! have had some plumbling problems - saggy pipes in basement caused backup in bathroom/kitchen of kitchen waste. but it's been fixed and haven't had a problem in 4 years.
any advice on what could be causing it and a cheap easy DIY solution?