I'm assuming that you do at least have a water level skimmer? If so, then read on. If it's only a bottom filter, then I have no idea. What size pool is it?
If it's a really small pool, then you may simply have to drain it out once in awhile. But if it's anything more than 500 gallons, then forget it.
Go to any pool supply shop (like Leslies). You can get a long hose, a vacuum brush and a pole and a fitting that will allow you to fit the hose directly to the filter intake. Then vacuum as normal.
That's what I did when I lived with my dad and he had his "dough boy" pool.