one of the guys over on icmag that helped me a ton when i moved to flood and drain said he uses a watering wand and just runs water through them during maintenance.
here is what he said when i asked about buildup and flushing.
“Yes I do. I use a hose and plain water to rinse out the pots every 2 weeks when I do a nute change. Not that it’s really needed but it’s a habit I started years ago. I used to only flush once a month but figured since I’m cleaning the table and res I might as well flush out the pots too. Then when plants are done I flush for 5 to 7 days or until my ph and ppm stay the same as what I started with.”
he uses fabric pots as well and said he gets the outside of the pots as well to ensure the salts are being washed away.
as i said before i do it a few times/run. maybe monthly as he mentions. in my garden with my nutrients and situation, i wouldn’t do it any less frequent than that or i get issues. tbh, if i didn’t have to drive across 2 cities to get to my room, i would do it weekly. i think if you do it every week or two, you will not need nearly as much water as you had to use this first time because you won’t be letting much build up between flushes.
i hope things work out and i will definitely be watching.