When your filtration pump runs it cycles the water through a filtration vessel which contains layers of sand in finer graduations or other granular material and this catches most debris. This debris is caught in the layers of sand so occasionally the cycle needs to be reversed or "backwashed" out of a waste tube which then flushes it out. Most sand filters contain pressure guages rated in PSI and the pool will generally run at 1-2PSI - when the gauge reaches 8PSI it is time to backwash - (making sure to turn the filtration pump off first before you set it in backwash mode!).

There are systems which enable control of the filtration vessel themselves - enabling the user to remotely backwash the pool - but this just depends on how far you want to go. When you are away from your holiday home, backwashing once a month (by your gardener?) will do just fine...

Sometimes rubbish settles on the bottom and the sides of the pool and this needs to be effectively "hoovered" up. There are two types of devices for this - one connects inline to your filtration pump and system and uses the water pressure to suck and move around the pool which accumulates the debris in the sand filter - another is an autonomous device or robot that has its own filtration bag which needs to be emptied occasionally. Both can be left in the pool for weeks or months at a time.