I use an external pump that is designed as a heavy duty draining pump. Hook it up to a hose and put it in the tank and pumps out ≈ 100 gallons in about 5-10 mins.
I also use a pond pump that I drop in my 246 gallon and it drops the level by half in around 7 min. I do 50 percent twice a week... I am running a 75 gallon sump.
I have a 180.. ok not 240+ but I have 6 tanks and the 180 is the largest. I also need to run a 100ft python for the change.. so needless to say I do it once a week! I can also not do the 180 within 3-4 hrs of doing the other tanks in the house or I run out of hot water... Soon as I can get a sink in the basement or even taps and a drain... where it doesn't mean dealing with 100ft of hose ill do it more often..