Back wash to waste

[Watermom]

Yes, you will lose quite a bit of water when vacuuming to waste. Try and scoop out as much debris with a net as you can before you start vacuuming. You may be able to get most of the solid debris out. Also, go ahead and take the chlorine up to shock level and let it start doing its thing. Actually, as the chlorine starts to work, your water may clear up pretty fast and you may find that there isn't as much in there as you might think. If you can get the leaves out manually, bleach will take care of the algae.

[waste]

Let's be sure of our terms here - I hope you mean 'vacuum to waste' and not vacuum to backwash. The former will bypass the filter, preventing the need to backwash - the latter will scr*w up the filter very quickly by putting the dirt on the wrong side of the filter media.

A time honored trick to vacuuming to 'me' () is to run the filter while brushing the pool, then, after an hour or 2, turn off the pump overnight. This will let the liberated debris settle into the usual 'low flow' spots in the pool where dirt usually accumulates, allowing you to vac to waste the majority of the debris in a short time, thereby loosing less water.

As Lisa said, get as much of the large debris out of there first!

[Poconos]

A trick I use with my pool is to rig the vacuum hose to one of the returns so it blows. In the PVC section of Home Depot you can adapt almost anything to anything. Then I go around the pool with the vacuum head, which is now blowing a jet of water, and stir up all the dust and any algae that's forming. This hits stuff that may not be easily reached by a brush too. Blow it into suspension. When I'm done that you can either do as Ted suggested or sometimes I just connect the vacuum up normally to the skimmer and leave the brush in the deep end making a temporary main drain. The stuff in suspension then gets sucked into the filter. WATCH THE PRESSURE though as sometimes with a lot of fine stuff the filter will plug easily.
Al