From day one of water changing I use this method
Equipment
2 x 30lt carbouys (plastic containers with screw cap), step ladder, short bungie and a gravel vac.
Gravel vac the water from the tank into carbouy (lower than tank)
Place other carbouy with new, dechlorinised water at top of step ladder (higher than tank) and secure through handle to ladder with bungie.
Syphon new water back into tank.
3 tips with this method I'd like to add.
1) Before starting to gravel vac the old water into the carbouy have a litre or so of water already in the carbouy so you end up taking slightly less water out than you put in to allow for water loss as condensation between water changes.
2) Mark the carbouys as old and new, that way the same one is used each time to collect the sludge.
3) If you have a spare heater (I use a small 50w) it can be placed in the new water carbouy during the night before water changing to bring it up to temperature thus minimising stress to fish during water changing.
Simple method.....longwinded explination