Do you have a hot tub or pool with the SPA FROG Ease In-Line System? Print this and fill/refill with your own chemicals. I use it with Bromine tablets.

I strongly recommend printing with PETG, ABS could also work. Avoid PLA for this.
Print without supports, 0.2mm.

Ultimaker

Ultimaker 3 Extended

Doesn't Matter

No

0.2

None

Drill one or more small holes to get the water flow you need. If you drill too much, use silicone sealant to block the hole and drill a new smaller hole.