if i use toilet paper to blow my nose, what is better for the enviroment-flushing to sewage plant or garbage?

Flush it. It is biodegradeable. If it goes to the dump it will be buried and will take years to disintegrate.

What an interesting question... Aside from the fact that it really doesn't matter (the impact of a few squares of TP on the environment is precisely squat compared to many other impacts of human living), the more important issue is how our actions affect our own systems for processing waste. Landfills are easier and less costly to create and sustain relative to treatment plants. Thus, I'd say it's better to toss it than flush it. As for the environment, you could argue the merits of one or the other forever but you'd never be able to prove which is better.

The best is to compost it if you can at your home, or in a compost bin that is picked up. If you can't, then flush it. The gas to transport all those tissues, and the space it takes up in landfills will be more than in a sewage plant.

However, the difference you make is trivial, and it would be more beneficial if you did something like composted food scraps, or recycled everything you can, including things other than common recyclables. Visit: http://www.earth911.com/ to find out more.