I am bad about cleaning mine out on a regular basis, but when I do I use a wet/dry shop vac to vacumm out the debris; then replace the amount of water that was removed with newly mixed up saltwater.
I do it once a month, using an old filter I vacuum out the bottom, of which mine has no sand so I don't worry about sucking that up. Just get the garbage out.
I keep a power head in the sump to minimize the amount of crud that settles. About once a month I'll siphon out the dead spots while doing a water change.
I do it about every two weeks . It collects in two areas in my sump .
I wipe salt creep down once a month with a vinegar paper towel.
I suck the stuff out with a python hose taking about 10% total water volume out .
I replace with newly mixed saltwater . Accomplishes two things at the same time.
Keeping it clean is the key to this hobby lol. I usually use a syphon or a shop vac depending on how dirty it gets and make sure i wipe off all of the salt creep.