We’ve never understood this one, but it gets asked more often than not, so take comfort in the fact that you are definitely not the first person to ask.  The answer is that it isn’t very practical.  The human remains are more sizable than you may think, and are not fluffy ash.  If you choose to flush them, it’s likely that it will be tedious and you may incur a plumber’s bill larger than the crematory bill.  From the environmental perspective, keep in mind that you are going to be flushing the toilet quite a few times.