What's the right way to flush out jetted tub lines?

That gray flaky stuff is biofilm sloughing off the inside of the recirculation lines. Every jetted tub holds a few quarts of stale water in the loop after you drain it, and with kids bathing daily the bathwater is basically a nutrient soup for it. The faint musty smell after running the jets is the same story. If it's flakes and strings rather than actual worms, you're dealing with gunk, not pests, which is the better outcome. Still, if you ever see anything that looks like it's moving, that's a diffrent problem and prolly means drain flies breeding in the sludge, and it'll take more than one flush to beat it.

I worry about this all the time with my deep soaking tub, even though it doesn't have jets. I've noticed a slight sludge build up around the drain opening sometimes. I guess I'm just paranoid that the lines are getting clogged inside the wall and that stuff is just slowly migrating out eventually. My plumbing is pretty old, so I worry about any internal corrosion.

Have any of you found that running a vinegar solution through the lines is as effective as a commercial cleaner? I don't want to damage the paint on the tub, but I also don't want to just ignore it til a proffesional has to come out to fix it.

I have a similar issue in my normal bathtub, not one of those fancy ones. When I clear the drain, sometimes there is some wierd gray gunk floating right out with the water. I just worry about what is going to happen deep inside the wall pipes over time. It is a bit gross to see that all the time. Does that kind of buildup just happen because of the older pipes in the house?

I have found that a significant portion of the gunk isn't organic growth at all, but rather a chemical reaction occurring within the plumbing that we colloquially call scale. When certain surfactants in standard bathroom soaps meet the mineral content of hard water, they precipitate out of solution, creating a soap scum that adheres to the internal surfaces of the lines and eventually washes out in those grey stringy clumps you described. Have you considered the pH level of the specific cleaning products you might be using, as certain alkaline cleaners can accelerate the deposition of these mineral solids over time? It is a distinct difference from true microbial growth in the pipes.

I had a battle with this exact issue on a house of mine, and the flushing approach never really solved it. What made the difference was using a diluted acetic acid solution every couple of months. I'd pour it into the jets and let it sit for an hour before running the tub to see what came out. It didn't dissolve the stuff, but it definitely broke up the buildup that was clinging to the chrome and inside the nozzles. It's a bit messy, but it keeps the lines from getting completley choked up. What kind of pH is your water usually before things start acting up?

Update: I ran the low water cycle with a squirt of dish soap, then a plain rinse cycle. First run pushed out way more of that gray sludge than I expected, second run came out mostly clean. But one reply said some of this gunk is soap and hard water reacting into scale, not living stuff. Does a detergent flush even touch that, or do I need an acidic run like vinegar for the mineral part?