Siphon's okay, but the easiest solution - and a good multi-purpose one - is to get a wet-dry vac from the hardware store. Set it in wet mode with all the extensions and you can stand on the side and it'll suck up everything pronto from the bottom corners and seat wells. It'll get pretty heavy in the base unit if you do it for very long, but it's easy to drain, and much easier than the grit-gitter, which looks like a toy to me.

I don't know. Dragging out the shop vac from the garage, runnig an extension cord, putting the hoses together, then putting it all away...rather time consuming and a PITA as far as I'm concerned!

For me, usually when I notice the grit, I'm in the hot tub., What could be easier than reaching out, grabbing the Grit-Gitter (hidden behind the planter), and, done in a couple of seconds.

Maybe you can get a self-suction cleaning kit from the dealer.