Toilets, Sinks, Showers, Tubs and Disposals - plumbing problem

We just moved into our house about 6 monthes ago... and we have a bathroom off of our kitchen. Every now and then, the toilet, after we flush won't flush all the way and then backs up. WE plunge and plunge and usually get it to work again. However, it seems that when we are having this problem, if I run the garbage disposal in the kitchen, all of the crushed up food comes up in the shower and has a terrible gas-sy odor and the seperate garden tub takes hours to drain. WE have a 1 year home warrenty on the plumbing - is this just a clog or possibly is there a problem in the plumbing. The house was built in the 20's but then completely gutted and an addition of about 1200sq feet was added (the bathroom that we have the problem with is in the addition) about 7 years ago. Any suggestions???

What you have is a serious problem with build up through out your plumbing system.A house that old is an obvious candidate for this problem.The addition of more plumbing and a garbage disposal has only made this situation worse.I would bet that,if the house was not replumbed during the addition,it still contains old galvanized piping and such which probably also has rust built up in it.Also the build up could be in the main outlet for all the drains.I would have a professional look your plumbing system over to determine exactly what you are dealing with from the standpoint of the types and ages of the piping and it's ability to be cleared using power augers.Drain cleaners and other consumer items are probably not going to solve this issue.This is an issue that has had 80 years to develop and was accelerated by adding to the system in recent years.